%I A091887
%S A091887 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,
%T A091887 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,
%U A091887 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
%N A091887 Irregularity index of the n-th irregular prime A000928(n).
%C A091887 See A091888 for definition.
%D A091887 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.
%H A091887 T. D. Noe, <a href="b091887.txt">Table of n, a(n) for n=1..10000</a> 
               (from Buhler et al)
%t A091887 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&]
%Y A091887 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)).
%Y A091887 Sequence in context: A127937 A083911 A095827 this_sequence A144871 A066799 
               A037832
%Y A091887 Adjacent sequences: A091884 A091885 A091886 this_sequence A091888 A091889 
               A091890
%K A091887 nonn
%O A091887 1,8
%A A091887 T. D. Noe (noe(AT)sspectra.com), Feb 09 2004