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%I #11 Nov 27 2014 15:29:58
%S 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,
%T 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,
%U 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
%N Irregularity index of the n-th irregular prime A000928(n).
%C See A091888 for definition.
%H T. D. Noe, <a href="/A091887/b091887.txt">Table of n, a(n) for n=1..10000</a> (from Buhler et al.)
%H J. Buhler, R. Crandall, R. Ernvall, T. Metsankyla and M. A. Shokrollahi, <a href="http://dx.doi.org/10.1006/jsco.1999.1011">Irregular Primes and Cyclotomic Invariants to 12 Million</a>, J. Symbolic Computation 31, 2001, 89-96.
%t 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 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)).
%K nonn
%O 1,8
%A _T. D. Noe_, Feb 09 2004
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