A078305 - OEIS

A078305

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

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

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OFFSET

1,1

COMMENTS

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

LINKS

MATHEMATICA

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}]

CROSSREFS

KEYWORD

nonn,base,more

AUTHOR

EXTENSIONS

Extended by Robert G. Wilson v and Jason Earls, Dec 24 2002

a(19)-a(20) from Michael S. Branicky, Jul 23 2023

STATUS

approved