A157833 - OEIS

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, 8275

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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

EXAMPLE

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

CROSSREFS

KEYWORD

nonn,more

AUTHOR

EXTENSIONS

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

a(16) from Michael S. Branicky, Aug 30 2024

STATUS

approved