A091909 Numbers n such that (2*n)!/(2*n!)+1 is prime.

1, 2, 3, 5, 6, 11, 12, 36, 95, 372, 842, 2196, 4755

Offset

1,2

Comments

a(14) > 10000. - Hugo Pfoertner, Jul 15 2019

Links

Table of n, a(n) for n=1..13.

Example

a(3)=3 because (2*3)!/(2*3!)+1=720/12+1=61 is prime.

Crossrefs

Cf. A091907.

Sequence in context: A081026 A137808 A275525 * A171040 A317256 A100883

Adjacent sequences: A091906 A091907 A091908 * A091910 A091911 A091912

Keyword

nonn,more,hard

Author

Hugo Pfoertner, Feb 10 2004

Extensions

a(12) and a(13) from Hugo Pfoertner, Jul 15 2019

Status

approved