A202423 - OEIS

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A202423

Numbers k such that k!*k!! + 1 is prime.

1

1, 2, 3, 4, 5, 14, 37, 48, 50, 52, 88, 223, 7450, 8427

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OFFSET

1,2

LINKS

Table of n, a(n) for n=1..14.

EXAMPLE

For k = 3, 3!*3!! + 1 = 6*3 + 1 = 19 is prime.

MATHEMATICA

lst={}; Do[If[PrimeQ[n!*n!!+1], AppendTo[lst, n]], {n, 500}]; lst

CROSSREFS

Cf. A000142, A006882, A202422.

Sequence in context: A361947 A037340 A199165 * A171593 A382803 A227535

Adjacent sequences: A202420 A202421 A202422 * A202424 A202425 A202426

KEYWORD

nonn,more,hard

AUTHOR

Michel Lagneau, Dec 19 2011

EXTENSIONS

a(13)-a(14) from Michael S. Branicky, Oct 25 2025

STATUS

approved