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

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

Offset

1,2

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

Links

Table of n, a(n) for n=1..7.

Example

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

Mathematica

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

Prog

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

Crossrefs

Cf. A008578, A138523.

Sequence in context: A084853 A115337 A114333 * A076209 A037399 A220891

Adjacent sequences: A265095 A265096 A265097 * A265099 A265100 A265101

Keyword

nonn,fini,full

Author

Altug Alkan, Dec 01 2015

Status

approved