A068206 - OEIS

A068206

Let N(2n) denote the numerator of B(2n), the 2n-th Bernoulli number and D(2n) the denominator; sequence gives values of n such that gcd(N(2n),D(2n-2))=7.

7, 28, 49, 70, 112, 133, 154, 196, 217, 238, 259, 280, 301, 322, 343, 364, 406, 427, 448, 469, 490, 511, 553, 574, 658, 679, 700, 721, 742, 763, 784, 826, 847, 868, 889, 910, 931, 952, 973, 994, 1036, 1057, 1078, 1099, 1120, 1141, 1162, 1204, 1246, 1267

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OFFSET

1,1

COMMENTS

a(n)==0 (mod 7). - Labos Elemer

Conjecture: All terms are of the form 7 + 21*j. - Vaclav Kotesovec, Apr 29 2014

LINKS

Vaclav Kotesovec, Table of n, a(n) for n = 1..4048

Vaclav Kotesovec, Graph of a(n)/n. Limit of a(n)/n (if it exists) is not 21, but ~ 25.9...

MATHEMATICA

Select[21*Range[0, 100]+7, GCD[Numerator[BernoulliB[2#]], Denominator[BernoulliB[2#-2]]]==7&] (* Vaclav Kotesovec, Apr 29 2014 *)

PROG