A110337 a(n) = 2n+1 if 2n+1 is prime else a(n) = least prime of the form (2n+1)(2n+3)...(2n+2k-1) + 2.

3, 5, 7, 101, 11, 13, 257, 17, 19, 9454727, 23, 677, 801011, 29, 31, 42737, 1297, 37, 1601, 41, 43, 5285387, 47, 410006013351009077, 148667, 53, 3137, 56284059197, 59, 61, 1529270318745462748663049625086428127, 4357, 67, 26822027, 71, 73

Offset

1,1

Links

Table of n, a(n) for n=1..36.

Example

a(4) = 9*11+2= 101, as 9 is composite.

Prog

(PARI) a(n) = {pr = 2*n+1; if (isprime(pr), return (pr)); pa = pr; ok = 0; while (! ok, pa += 2; pr *= pa; ok = isprime(pr + 2); ); pr + 2; } \\ Michel Marcus, Sep 16 2013

Crossrefs

Cf. A110336.

Sequence in context: A051345 A242387 A104388 * A132287 A046201 A374101

Adjacent sequences: A110334 A110335 A110336 * A110338 A110339 A110340

Keyword

nonn

Author

Amarnath Murthy, Jul 20 2005

Extensions

More terms from Victoria Sapko (vsapko(AT)frc.mass.edu), Sep 28 2007

Corrected and extended by Michel Marcus, Sep 16 2013

Status

approved