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The On-Line Encyclopedia of Integer Sequences (OEIS), also cited simply as Sloane's, is an online database of integer sequences, created and maintained by N. J. A. Sloane, a researcher at AT&T Labs. In October 2009, the intellectual property and hosting of the OEIS were transferred to the OEIS Foundation.^{[2]} OEIS records information on integer sequences of interest to both professional mathematicians and amateurs, and is widely cited. As of 24 January 2013^{[update]} it contains over 220,000 sequences, making it the largest database of its kind.
Each entry contains the leading terms of the sequence, keywords, mathematical motivations, literature links, and more, including the option to generate a graph or play a musical representation of the sequence. The database is searchable by keyword and by subsequence.
Neil Sloane started collecting integer sequences as a graduate student in 1965 to support his work in combinatorics. The database was at first stored on punch cards. He published selections from the database in book form twice:
These books were well received and, especially after the second publication, mathematicians supplied Sloane with a steady flow of new sequences. The collection became unmanageable in book form, and when the database had reached 16,000 entries Sloane decided to go online—first as an e-mail service (August 1994), and soon after as a web site (1996). As a spin-off from the database work, Sloane founded the Journal of Integer Sequences in 1998.^{[3]} The database continues to grow at a rate of some 10,000 entries a year. Sloane has personally managed 'his' sequences for almost 40 years, but starting in 2002, a board of associate editors and volunteers has helped maintain the database.^{[4]} In 2004, Sloane celebrated the addition of the 100,000th sequence to the database,
Besides integer sequences, the OEIS also catalogs sequences of fractions, the digits of transcendental numbers, complex numbers and so on by transforming them into integer sequences. Sequences of rationals are represented by two sequences (named with the keyword 'frac'): the sequence of numerators and the sequence of denominators. For example, the fifth order A006843). Important irrational numbers such as π = 3.1415926535897... are catalogued under representative integer sequences such as decimal expansions (here 3, 1, 4, 1, 5, 9, 2, 6, ... (A001203)).
The OEIS is currently limited to plain ASCII text, so it uses a linear form of conventional mathematical notation (such as f(n) for functions, n for running variables, etc.). Greek letters are usually represented by their full names, e.g., mu for μ, phi for φ. Every sequence is identified by the letter A followed by six digits, sometimes referred to without the leading zeros, e.g., A315 rather than A000315. Individual terms of sequences are separated by commas. Digit groups are not separated by commas, periods, or spaces. In comments, formulas, etc., a(n) represents the nth term of the sequence.
Zero is often used to represent non-existent sequence elements. For example, magic square of least magic constant, or 0 if no such magic square exists." The value of a(1) (a 1×1 magic square) is 2; a(3) is 1480028129. But there is no such 2×2 magic square, so a(2) is 0. This special usage has a solid mathematical basis in certain counting functions. For example, the A014197) counts the solutions of φ(x) = m. There are 4 solutions for 4, but no solutions for 14, hence a(14) of A014197 is 0—there are no solutions. Occasionally −1 is used for this purpose instead, as in A094076.
The OEIS maintains the lexicographical order of the sequences, so each sequence has a predecessor and a successor (its "context"). OEIS normalizes the sequences for lexicographical ordering, (usually) ignoring all initial zeros and ones, and also the sign of each element. Sequences of weight distribution codes often omit periodically recurring zeros.
For example, consider: the prime numbers, the palindromic primes, the Fibonacci sequence, the lazy caterer's sequence, and the coefficients in the series expansion of $\backslash textstyle$. In OEIS lexicographic order, they are:
whereas unnormalized lexicographic ordering would order these sequences thus: #3, #5, #4, #1, #2.
Very early in the history of the OEIS, sequences defined in terms of the numbering of sequences in the OEIS itself were proposed. "I resisted adding these sequences for a long time, partly out of a desire to maintain the dignity of the database, and partly because A22 was only known to 11 terms !" Sloane reminisced.^{[9]} One of the earliest self-referential sequences Sloane accepted into the OEIS was A000022. Some sequences are both finite and listed in full (keywords "fini" and "full"); these sequences will not always be long enough to contain a term that corresponds to their OEIS sequence number. In this case the corresponding term a(n) of A091967 is undefined. A100544 lists the first term given in sequence A_{n}, but it needs to be updated from time to time because of changing opinions on offsets. Listing instead term a(1) of sequence A_{n} might seem a good alternative if it weren't for the fact that some sequences have offsets of 2 and greater. This line of thought leads to the question "Does sequence A_{n} contain the number n ?" and the sequences A002808 is the sequence of composite numbers, while the non-prime 40 is in A053169 because it's not in A000040, the prime numbers. Each n is a member of exactly one of these two sequences, and in principle it can be determined which sequence each n belongs to, with two exceptions (related to the two sequences themselves):
This entry, A046970, was chosen because it contains every field an OEIS entry can have.
A046970 Generated from Riemann Zeta function: coefficients in series expansion of Zeta(n+2)/Zeta(n). 1, -3, -8, -3, -24, 24, -48, -3, -8, 72, -120, 24, -168, 144, 192, -3, -288, 24, -360, 72, 384, 360, -528, 24, -24, 504, -8, 144, -840, -576, -960, -3, 960, 864, 1152, 24, -1368, 1080, 1344, 72, -1680, -1152, -1848, 360, 192, 1584, -2208, 24, -48, 72, 2304, 504, -2808, 24, 2880, 144, 2880, 2520, -3480, -576 OFFSET 1,2 COMMENTS B(n+2) = -B(n)*((n+2)*(n+1)/(4pi^2))*z(n+2)/z(n) = -B(n)*((n+2)*(n+1)/(4pi^2))*Sum(j=1, infinity) [ a(j)/j^(n+2) ] ... REFERENCES M. Abramowitz and I. A. Stegun, Handbook of Mathematical Functions, Dover Publications, 1965, pp. 805-811. LINKS M. Abramowitz and I. A. Stegun, eds., Handbook of Mathematical Functions, National Bureau of Standards, Applied Math. Series 55, Tenth Printing, 1972 [alternative scanned copy]. World Heritage Encyclopedia, Riemann zeta function. FORMULA Multiplicative with a(p^e) = 1-p^2. a(n) = Sum_{d|n} mu(d)*d^2. a(n) = product[p prime divides n, p^2-1] (gives unsigned version) [From Jon Perry (jonperrydc(AT)btinternet.com), Aug 24 2010] EXAMPLE a(3) = -8 because the divisors of 3 are {1, 3} and mu(1)*1^2 + mu(3)*3^2 = -8. ... MAPLE Jinvk := proc(n, k) local a, f, p ; a := 1 ; for f in ifactors(n)[2] do p := op(1, f) ; a := a*(1-p^k) ; end do: a ; end proc: A046970 := proc(n) Jinvk(n, 2) ; end proc: # R. J. Mathar, Jul 04 2011 MATHEMATICA muDD[d_] := MoebiusMu[d]*d^2; Table[Plus @@ muDD[Divisors[n]], {n, 60}] (Lopez) Flatten[Table^2 - 1)]; p}, {n, 1, 50, 1}]] [From Jon Perry (jonperrydc(AT)btinternet.com), Aug 24 2010] PROG (PARI) A046970(n)=sumdiv(n, d, d^2*moebius(d)) (Benoit Cloitre) CROSSREFS Cf. A027641 and A027642. Sequence in context: A035292 A144457 A146975 * A058936 A002017 A118582 Adjacent sequences: A046967 A046968 A046969 * A046971 A046972 A046973 KEYWORD sign,mult AUTHOR Douglas Stoll, dougstoll(AT)email.msn.com EXTENSIONS Corrected and extended by Vladeta Jovovic (vladeta(AT)eunet.rs), Jul 25 2001 Additional comments from Wilfredo Lopez (chakotay147138274(AT)yahoo.com), Jul 01 2005
See Format of OEIS Pages.
The previous version of the main look-up page of the OEIS offered three ways to look up sequences, and the right radio button had to be selected. There was an advanced look-up page, but its usefulness has been integrated into the main look-up page in a major redesign of the interface in January 2006.
Enter a few terms of the sequence, separated by either spaces or commas (or both). You can enter negative signs, but they will be ignored. For example, 0, 3, 7, 13, 20, 28, 36, 43, 47, 45, 32, 0, −64, n^{2} minus the nth Fibonacci number, is a sequence that is technically not in the OEIS, but the very similar sequence 0, −3, −7, −13, −20, −28, −36, −43, −47, −45, −32, 0, 64, is in the OEIS and will come up when one searches for its reversed signs counterpart. However, the search can be forced to match signs by using the prefix "signed:" in the search string. This is especially useful for sequences like A008836 that consist exclusively of positive and negative ones. One can enter as little as a single integer or as much as four lines of terms. Sloane recommends entering six terms, a(2) to a(7), in order to get enough results, but not too many results. There are cases where entering just one integer gives precisely one result, such as 6610199 brings up just strobogrammatic primes which are not palindromic). There are also cases where one can enter many terms and still not narrow the results down very much.
Enter a string of alphanumerical characters. Certain characters, like accented foreign letters, are not allowed. Thus, to search for sequences relating to Znám's problem, try enter it without the accents: "Znam's problem." The handling of apostrophes has been greatly improved in the 2006 redesign. The search strings "Pascal's triangle," "Pascals triangle" and "Pascal triangle" all give the desired results. To look up most polygonal numbers by word, try "n-gonal numbers" rather than "Greek prefix-gonal numbers" (e.g., "47-gonal numbers" instead of "heptaquartagonal numbers"). Beyond "dodecagonal numbers," word searching with the Greek prefixes might fail to yield the desired results.
Enter the modern OEIS A number of the sequence, with the letter A and with or without zero-padding. As of 2006, the old M and N sequence numbers will yield the proper result as search strings, e.g., a search for M0422 will correctly bring up A000422, concatenation of numbers from n down to 1.
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