A265098 Integers n such that A138523(n) is 1 or a prime.

1, 2, 3, 4, 5, 28, 32

Offset: 1

Author

Altug Alkan, Dec 01 2015

Keywords

• nonn
• fini
• full

Comments

Inspired by the following triangle for the initial terms:

1! = 1.

1! + 3! = 7.

1! + 3! + 5! = 127.

1! + 3! + 5! + 7! = 5167.

1! + 3! + 5! + 7! + 9! = 368047.

This sequence is finite since 107 divides A138523(n) for all n >= 53. - Amiram Eldar, Apr 20 2017

Examples

			a(4) = 4 because 1! + 3! + 5! + 7! = 5167 is prime.
		

Crossrefs

Cf. A008578, A138523.

Programs

Mathematica

Select[Range@ 1000, Or[# == 1, PrimeQ@ #] &@ Sum[(2 k - 1)!, {k, #}] &] (* Michael De Vlieger, Dec 01 2015 *)

PARI

lista(nn) = { print1(1, ", "); s = 0; for(k=1, nn, s += (2*k-1)!; if(ispseudoprime(s), print1(k, ", ")); ); }