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

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

(PARI) isok(n) = gcd(numerator(bernfrac(2*n)), denominator(bernfrac(2*n-2))) == 7; \\ Michel Marcus, Mar 06 2014

Crossrefs

Cf. A068528.

Sequence in context: A321777 A269451 A139607 * A118120 A078307 A045551

Adjacent sequences: A068203 A068204 A068205 * A068207 A068208 A068209

Keyword

easy,nonn

Author

Benoit Cloitre, Mar 23 2002

Status

approved