A255924 - OEIS

A255924

Bases b for which exactly three Wieferich primes p with p < b exist such that p is a base-b Wieferich prime.

19, 28, 53, 68, 80, 89, 107, 129, 137, 143, 145, 146, 147, 148, 170, 177, 181, 197, 215, 224, 253, 263, 268, 299, 307, 324, 332, 333, 334, 339, 341, 349, 350, 354, 357, 359, 360, 362, 368, 373, 377, 389, 393, 399, 402, 403, 410, 413, 437, 440, 449, 451, 457

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OFFSET

1,1

COMMENTS

Numbers b such that A255920(b) = 3.

LINKS

Felix Fröhlich, Table of n, a(n) for n = 1..10000

Eric Weisstein's World of Mathematics, Wieferich Prime

PROG

(PARI) is(n) = my(i=0); forprime(p=1, n-1, if(Mod(n, p^2)^(p-1)==1, i++); if(i > 3, return(0))); i==3

(Sage) [b for b in range(3, 458) if len([p for p in range(2, b) if is_prime(p) and mod(b, p^2)^(p-1)==1])==3] # Danny Rorabaugh, Mar 31 2015

CROSSREFS

Cf. A255920.

Cf. bases b with exactly k base-b Wieferich primes less than b: A255921 (k=0), A255922 (k=1), A255923 (k=2), A255925 (k=4), A325881 (k=5), A325882 (k=6), A325883 (k=7), A325884 (k=8), A325885 (k=9), A325886 (k=10).

Sequence in context: A369341 A368871 A120144 * A067452 A123944 A095046

Adjacent sequences: A255921 A255922 A255923 * A255925 A255926 A255927

KEYWORD

nonn

AUTHOR

Felix Fröhlich, Mar 23 2015

STATUS

approved