A078305 - OEIS

%I #14 Jul 23 2023 17:00:44

%S 3,4,5,6,7,13,14,19,20,28,37,99,100,108,141,304,442,682,3641,4076

%N Numbers k such that A004154(k) - 1 is prime.

%C Some of the larger entries may only correspond to probable primes.

%t f[n_] := n!/10^Sum[ Floor[n/5^k], {k, 1, Log[10, n] + 1}]; Do[ If[ PrimeQ[ f[n] - 1], Print[n]], {n, 1, 750}]

%Y Cf. A004154, A078154, A078203, A078190.

%K nonn,base,more

%O 1,1

%A _Cino Hilliard_, Dec 23 2002

%E Extended by _Robert G. Wilson v_ and _Jason Earls_, Dec 24 2002

%E a(19)-a(20) from _Michael S. Branicky_, Jul 23 2023