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A290839 a(n) = smallest prime p such that 2p + 2n - 1 is prime. 2

%I

%S 2,2,2,3,2,2,3,2,2,3,2,5,3,2,2,7,3,2,3,2,2,3,2,7,3,2,5,3,2,2,7,3,2,3,

%T 2,2,13,3,2,3,2,11,3,2,5,7,3,2,3,2,2,3,2,2,3,2,13,7,11,5,19,3,2,3,2,5,

%U 3,2,2,7,5,5,3,2,2,7,3,2,13,3,2,3,2,7,3,2

%N a(n) = smallest prime p such that 2p + 2n - 1 is prime.

%H Iain Fox, <a href="/A290839/b290839.txt">Table of n, a(n) for n = 0..20000</a>

%F a(-n) = A290838(n+1). - _Iain Fox_, Dec 14 2017

%t Table[j=0; found=False; While[!found, j++; found=PrimeQ[2Prime[j]+2n-1]]; Prime[j], {n, 85}]

%o (PARI) a(n) = {my(p=2); while(!isprime(2*p+2*n-1), p = nextprime(p+1)); p;} \\ _Michel Marcus_, Aug 12 2017

%Y Cf. A005384, A023204, A023205, A023206, A023207, A171517, A020483, A290838.

%Y Cf. A067076 (indices n at which a(n) = 2).

%K nonn,easy

%O 0,1

%A _XU Pingya_, Aug 12 2017

%E a(0) prepended by _Iain Fox_, Dec 14 2017

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Last modified September 19 04:30 EDT 2019. Contains 327187 sequences. (Running on oeis4.)