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

1,1

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

Formula

a(n) = A010879(A000928(n)). - Amiram Eldar, Jul 02 2024

Example

a(6) = 1 because the 6th irregular prime is 131 and 131 mod 10 = 1.

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 *)

Crossrefs

Cf. A000928, A010879.

Sequence in context: A239069 A154168 A019644 * A194641 A248674 A108743

Adjacent sequences: A100636 A100637 A100638 * A100640 A100641 A100642

Keyword

easy,nonn

Author

Pahikkala Jussi, Dec 04 2004

Extensions

More terms from Robert G. Wilson v, Dec 10 2004

Status

approved