This site is supported by donations to The OEIS Foundation.

 Annual Appeal: Please make a donation to keep the OEIS running. In 2018 we replaced the server with a faster one, added 20000 new sequences, and reached 7000 citations (often saying "discovered thanks to the OEIS"). Other ways to donate

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A249306 Denominators A027642(n) of Bernoulli numbers except for a(4*k+5)=2 instead of 1. 1
 1, 2, 6, 1, 30, 2, 42, 1, 30, 2, 66, 1, 2730, 2, 6, 1, 510, 2, 798, 1, 330, 2, 138, 1, 2730, 2, 6, 1, 870, 2, 14322, 1, 510, 2, 6, 1, 1919190, 2, 6, 1, 13530, 2, 1806, 1, 690, 2, 282, 1, 46410, 2, 66, 1, 1590, 2, 798, 1, 870, 2, 354, 1 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS There exist an infinity of 1's, 2's, 6's, 30's, 42's, 66's, ... . Respective ranks:    0,   3,    7,   11,   15,   19, ...    1,   5,    9,   13,   17,   21, ...   (= A016813)    2,  14,   26,   34,   38,   62, ...   (= A051222)    4,   8,   68,   76,  124,  152, ...   (= A051226)    6, 114,  186,  258,  354,  402, ...   (= A051228)   10,  50,  170,  370,  470,  590, ...   (= A051230)   12,  24, 1308, 1884, 2004, 2364, ...   (= A249134)   etc. Hence by antidiagonals a permutation of A001477(n). First column: A248614(n). a(n) is an alternative sequence for the denominators of the Bernoulli numbers. First 36 terms of the corresponding clockwise spiral: .   330------2----138------1---2730------2     |                                  |     |                                  |     1     42------1-----30------2      6     |      |                    |      |     |      |                    |      |   798      2      1------2     66      1     |      |             |      |      |     |      |             |      |      |     2     30------1------6      1    870     |                           |      |     |                           |      |   510------1------6------2---2730      2                                        |                                        |     1------6------2----510------1--14322 LINKS FORMULA a(2n) = A002445(n), a(2n+1) = A000034(n+1). MAPLE Clausen := proc(n) local S, i; S := numtheory[divisors](n); S := map(i->i+1, S); S := select(isprime, S); mul(i, i=S) end: A249306 := n -> `if`(n mod 4 = 3, 1, Clausen(n)): seq(A249306(n), n=0..59); # Peter Luschny, Nov 10 2014 MATHEMATICA a[n_] := Denominator[BernoulliB[n]]; a[n_ /; Mod[n, 4] == 1] = 2; Table[a[n], {n, 0, 60}] (* Jean-François Alcover, Oct 28 2014 *) CROSSREFS A variant of the Clausen numbers A141056, A160014. And of A176591. Cf. A000034, A002445, A016813, A027642, A051222, A051226, A051228, A051230, A090126, A164020, A248614, A249134. Sequence in context: A132181 A291646 A027642 * A117214 A185972 A182918 Adjacent sequences:  A249303 A249304 A249305 * A249307 A249308 A249309 KEYWORD nonn AUTHOR Paul Curtz, Oct 28 2014 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified December 13 22:07 EST 2018. Contains 318087 sequences. (Running on oeis4.)