A289754 Primes of the form k!10 - 1, where k!10 is the decuple factorial number (A288327).

2, 3, 5, 7, 23, 199, 239999, 7354367, 719999999, 2287853567, 50399999999, 43193222037503, 199094626418687, 17254743876205585224626400657407, 620448401733239439359999999999999999999999999999, 17999257015554062631539656405422901164857242675052543

Offset: 1

Author

Robert Price, Jul 11 2017

Keywords

• nonn

Links

• Robert Price, Table of n, a(n) for n = 1..18
• Henri and Renaud Lifchitz, PRP Records.Search for n!10-1.
• Joe McLean, Interesting Sources of Probable Primes.
• OpenPFGW Project, Primality Tester.

Crossrefs

Cf. A204658, A288327.

Programs

Mathematica

MultiFactorial[n_, k_] := If[n<1, 1, n*MultiFactorial[n-k, k]];
Select[Table[MultiFactorial[i, 10] - 1, {i, 2, 100}], PrimeQ[#]&]

Formula

a(n) = A288327(A204658(n)) - 1. - Elmo R. Oliveira, Apr 14 2025