A089644 Numbers k such that 7 divides the numerator of B(2*k) where B(k) = the k-th Bernoulli number.

7, 14, 28, 35, 49, 56, 70, 77, 91, 98, 112, 119, 133, 140, 154, 161, 175, 182, 196, 203, 217, 224, 238, 245, 259, 266, 280, 287, 301, 308, 322, 329, 343, 350, 364, 371, 385, 392, 406, 413, 427, 434, 448, 455, 469, 476, 490, 497, 511, 518, 532, 539, 553, 560

Offset

1,1

Links

Amiram Eldar, Table of n, a(n) for n = 1..10000

Formula

a(n) = 7*A001651(n).

a(n) = 21*(n-1)-a(n-1), with n>1, a(1)=7. - Vincenzo Librandi, Nov 16 2010

Mathematica

Select[Range[500], Divisible[Numerator @ BernoulliB[2*#], 7] &] (* Amiram Eldar, May 17 2021 *)

Prog

(PARI) isok(n) = ! ((numerator(bernfrac(2*n))) % 7); \\ Michel Marcus, Dec 06 2013

Crossrefs

Cf. A001651, A027641, A027642, A073216.

Sequence in context: A115874 A083495 A185066 * A178335 A158204 A115815

Adjacent sequences: A089641 A089642 A089643 * A089645 A089646 A089647

Keyword

nonn,easy

Author

Benoit Cloitre, Jan 01 2004

Status

approved