A260531 - OEIS

%I #13 Aug 10 2015 16:35:19

%S 1,0,21,1,45,79,120,305,484,697,404,186,1354,603,612,2757,945,3051,

%T 3552,498,950,1186,2657,1781,6403,9192,8035,1927,2181,2713,6097,2621,

%U 10139,3476,10878,8608,22609,21028,24550,19031,1,12852,33426,27793,34279,11543

%N a(n) = (2^p+1)^(p-1) modulo p^2, where p is prime(n).

%C The primes where a(n) == 1 are given by A260507.

%H Felix Fröhlich, <a href="/A260531/b260531.txt">Table of n, a(n) for n = 1..10000</a>

%F  a(n) = A098640(n)^(A000040(n)-1) modulo A000040(n)^2.

%t f[n_] := Block[{p = Prime@ n}, PowerMod[2^p + 1, p - 1, p^2]]; Array[f, 46] (* _Robert G. Wilson v_, Jul 29 2015 *)

%o (PARI) a(n) = lift(Mod(2^prime(n)+1, prime(n)^2)^(prime(n)-1))

%Y Cf. A000040, A098640, A260507.

%K nonn

%O 1,3

%A _Felix Fröhlich_, Jul 28 2015