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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. 0

%I

%S 3,5,7,101,11,13,257,17,19,9454727,23,677,801011,29,31,42737,1297,37,

%T 1601,41,43,5285387,47,410006013351009077,148667,53,3137,56284059197,

%U 59,61,1529270318745462748663049625086428127,4357,67,26822027,71,73

%N 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.

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

%o (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

%Y Cf. A110336.

%K nonn

%O 1,1

%A _Amarnath Murthy_, Jul 20 2005

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

%E Corrected and extended by _Michel Marcus_, Sep 16 2013

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Last modified June 4 09:42 EDT 2020. Contains 334825 sequences. (Running on oeis4.)