A218755 Denominators of Bernoulli numbers which are == 6 (mod 9).

6, 42, 330, 510, 690, 798, 870, 1410, 1518, 1590, 1770, 1806, 2490, 3102, 3210, 3318, 3894, 4110, 4326, 4470, 4686, 5010, 5190, 5370, 5478, 6486, 6810, 7062, 7890, 8070, 8142, 8646, 8790, 9366, 9510, 10410, 10770, 11022

Offset

1,1

Comments

The sequence contains the elements of A090801 which are == 6 (mod 9).

Conjecture: all first differences 36, 288, 180, 180,... of the sequence are multiples of 36.

The conjecture is true, since elements of A090801 are 2 mod 4. - Charles R Greathouse IV, Nov 22 2012

Links

Charles R Greathouse IV, Table of n, a(n) for n = 1..10000

Mathematica

Take[Union[Select[Denominator[BernoulliB[Range[1000]]], Mod[#, 9]==6&]], 60] (* Harvey P. Dale, Nov 28 2012 *)

Prog

(PARI) is(n)=if(n%36-6, 0, my(f=factor(n)); if(vecmax(f[, 2])>1, return(0)); fordiv(lcm(apply(k->k-1, f[, 1])), k, if(isprime(k+1) && n%(k+1), return(0))); 1) \\ Charles R Greathouse IV, Nov 26 2012

Crossrefs

Second subset of the Bernoulli denominators: A090801 which are == 3 (mod 9).

Sequence in context: A118351 A033296 A364437 * A165314 A082302 A144223

Adjacent sequences: A218752 A218753 A218754 * A218756 A218757 A218758

Keyword

nonn,easy

Author

Paul Curtz, Nov 05 2012

Status

approved