1,1

For n=0 the expression equals 1 and has no prime factor at all.

The larger terms, and/or those ending in ...01, correspond to indices (listed in A237443) for which the expression itself is a prime (listed in A118812).

Table of n, a(n) for n=1..25.

(PARI) n -> factor((2*n)!-n!+1)[1, 1]

Cf. A237443, A118812.

Sequence in context: A162711 A120713 A167920 * A104644 A158992 A128365

Adjacent sequences: A237576 A237577 A237578 * A237580 A237581 A237582

nonn

M. F. Hasler, Feb 09 2014

approved