A157833 Numbers k such that 1 + Sum_{j=0..k} (-1)^j*(k-j)! is prime.

2, 3, 5, 7, 15, 19, 41, 59, 61, 105, 661, 2653, 3069, 3943, 4053

Offset

1,1

Comments

Note that when k is even, 3 divides the sum.

The sums corresponding to terms >= 661 are only probable primes. - Klaus Brockhaus, Mar 13 2009

Links

Table of n, a(n) for n=1..15.

Example

a(2) = ((-1)^0)(2-0)! + ((-1)^1)(2-1)! + ((-1)^2)(2-2)! + 1 = 2! - 1! + 0! + 1 = 3 (prime).

Crossrefs

Sequence in context: A303875 A331037 A228652 * A175758 A151531 A335203

Adjacent sequences: A157830 A157831 A157832 * A157834 A157835 A157836

Keyword

nonn,more

Author

Kyle D. Balliet, Mar 07 2009

Extensions

a(7)-a(15) from Klaus Brockhaus, Mar 13 2009

Status

approved