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A218755 Denominators of Bernoulli numbers which are == 6 (mod 9). 2
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 (list; graph; refs; listen; history; text; internal format)
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: A142985 A118351 A033296 * A165314 A082302 A144223

Adjacent sequences:  A218752 A218753 A218754 * A218756 A218757 A218758

KEYWORD

nonn,easy

AUTHOR

Paul Curtz, Nov 05 2012

STATUS

approved

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Last modified August 24 23:41 EDT 2019. Contains 326314 sequences. (Running on oeis4.)