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A178814 (n^(p-1) - 1)/p^2 mod p, where p is the first prime that divides (n^(p-1) - 1)/p. 1

%I

%S 0,487,4,974,1,30384,1,1,0,2,46,1571,1,17,24160,855,0,4,1,189,1,5,11,

%T 1,0,0,1,0,1,3,2,3,0,19632919407,1,60768,1,11,1435,8,0,0,2,2,1,1

%N (n^(p-1) - 1)/p^2 mod p, where p is the first prime that divides (n^(p-1) - 1)/p.

%C (n^(p-1) - 1)/p^2 mod p, where p is the first prime such that p^2 divides n^(p-1) - 1.

%C See references and additional comments, links, and cross-refs in A001220 and A039951.

%H Wikipedia, <a href="http://en.wikipedia.org/wiki/Fermat_quotient#Generalized_Wieferich_primes">Generalized Wieferich primes</a>

%F a(n) = (n^(p-1) - 1)/p^2 mod p, where p = A039951(n).

%F a(n) = k mod 2, if n = 4k+1.

%F a(prime(n)) = A178813(n).

%e The first prime p that divides (3^(p-1) - 1)/p is 11, so a(3) = (3^10 - 1)/11^2 mod 11 = 488 mod 11 = 4.

%Y a(2) = A178812(1) = A178813(1). Cf. A001220, A039951, A174422.

%K hard,more,nonn

%O 1,2

%A _Jonathan Sondow_, Jun 17 2010

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Last modified February 26 18:29 EST 2020. Contains 332293 sequences. (Running on oeis4.)