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 A100639 Residues modulo 10 of the irregular primes (A000928). 0
 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 (list; graph; refs; listen; history; text; internal format)
 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 EXAMPLE a(6) = 1 because the 6th irregular prime is 131. 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. 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

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