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%I #15 Jan 27 2021 05:14:47
%S 3,10,19,24,28,61,79,96,104,125,132,191,196,243,292,302,462,466,586,
%T 621,1508,3307,3823,4729,5370,6721,8110,11145,13502,13762,20266,27868,
%U 38522,75470
%N Numbers n such that 5^n mod 2^n is prime.
%C Here 'mod' denotes the binary modulo operation (nonnegative remainder).
%t fQ[n_] := PrimeQ@ PowerMod[5, n, 2^n]; k = 1; lst = {}; While[k < 17501, If[fQ@ k, AppendTo[lst, k]]; k++]; lst
%o (PARI) for(n=1,9999, ispseudoprime(5^n % 2^n) & print1(n",")) \\ _M. F. Hasler_, Jan 03 2011
%o (PARI) for(n=1,1e5,if(ispseudoprime(lift(Mod(5,2^n)^n)),print1(n", "))) \\ _Charles R Greathouse IV_, Oct 10 2011
%Y Cf. A178995.
%K nonn,hard
%O 1,1
%A _Robert G. Wilson v_, Jan 03 2011
%E a(31)-a(34) from _Charles R Greathouse IV_, Oct 10 2011