A091887 - OEIS

A091887

Irregularity index of the n-th irregular prime A000928(n).

1, 1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 2, 1, 1, 1, 1, 1, 1, 1, 2, 3, 1, 1, 2, 1, 1, 2, 1, 1, 1, 3, 1, 2, 3, 1, 1, 2, 1, 1, 2, 1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 1, 3, 1, 1, 1, 3, 1, 1, 1, 1, 2, 2, 1, 2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 2, 1, 2, 1, 1, 1

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OFFSET

1,8

COMMENTS

See A091888 for definition.

LINKS

T. D. Noe, Table of n, a(n) for n=1..10000 (from Buhler et al.)

J. Buhler, R. Crandall, R. Ernvall, T. Metsankyla and M. A. Shokrollahi, Irregular Primes and Cyclotomic Invariants to 12 Million, J. Symbolic Computation 31, 2001, 89-96.

MATHEMATICA

tp=Table[p=Prime[i]; cnt=0; k=1; While[2k<=p-3, If[Mod[Numerator[BernoulliB[2k]], p]==0, cnt++ ]; k++ ]; cnt, {i, 400}]; Select[tp, #>0&]

CROSSREFS

Cf. A073277 (primes having irregularity index 2), A060975 (primes having irregularity index 3), A061576 (least prime having irregularity index n), A091888 (irregularity index of prime(n)).

Sequence in context: A343639 A095827 A193582 * A144871 A066799 A238900

Adjacent sequences: A091884 A091885 A091886 * A091888 A091889 A091890

KEYWORD

nonn

AUTHOR

T. D. Noe, Feb 09 2004

STATUS

approved