A100639 Residues modulo 10 of the irregular primes (A000928).
7, 9, 7, 1, 3, 1, 9, 7, 3, 7, 3, 1, 3, 3, 7, 1, 7, 3, 9, 9, 1, 9, 1, 3, 1, 3, 7, 1, 3, 1, 7, 7, 7, 7, 3, 7, 3, 7, 9, 1, 7, 3, 9, 3, 7, 3, 1, 7, 1, 7, 1, 3, 7, 9, 1, 1, 7, 9, 7, 1, 7, 9, 3, 1, 1, 1, 7, 9, 1, 3, 3, 1, 7, 9, 7, 9, 3, 1, 7, 1, 7, 9, 7, 7, 1, 9, 9, 9, 3, 9, 3, 9, 7, 9, 3, 9, 1, 7, 3, 9, 1, 3, 3, 9, 7
Offset: 1
Examples
a(6) = 1 because the 6th irregular prime is 131 and 131 mod 10 = 1.
References
- Z. I. Borevich and I. R. Shafarevich, Number Theory. Academic Press, NY, 1966, pp. 425-430 (but there are errors).
Links
- Amiram Eldar, Table of n, a(n) for n = 1..10000
Programs
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Mathematica
fQ[n_] := Block[{p = n, k = 1}, While[ 2*k <= p - 3 && Mod[ Numerator[ BernoulliB[ 2*k ]], p ] != 0, k++ ]; 2k != p - 1]; Mod[ Select[ Prime[ Range[2, 275]], fQ[ # ] &], 10] (* Robert G. Wilson v, Dec 10 2004 *)
Formula
Extensions
More terms from Robert G. Wilson v, Dec 10 2004