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 A290839 a(n) = smallest prime p such that 2p + 2n - 1 is prime. 2
 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, 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, 3, 2, 2, 7, 5, 5, 3, 2, 2, 7, 3, 2, 13, 3, 2, 3, 2, 7, 3, 2 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,1 LINKS Iain Fox, Table of n, a(n) for n = 0..20000 FORMULA a(-n) = A290838(n+1). - Iain Fox, Dec 14 2017 MATHEMATICA Table[j=0; found=False; While[!found, j++; found=PrimeQ[2Prime[j]+2n-1]]; Prime[j], {n, 85}] PROG (PARI) a(n) = {my(p=2); while(!isprime(2*p+2*n-1), p = nextprime(p+1)); p; } \\ Michel Marcus, Aug 12 2017 CROSSREFS Cf. A005384, A023204, A023205, A023206, A023207, A171517, A020483, A290838. Cf. A067076 (indices n at which a(n) = 2). Sequence in context: A195352 A103507 A219252 * A085694 A258570 A257572 Adjacent sequences:  A290836 A290837 A290838 * A290840 A290841 A290842 KEYWORD nonn,easy AUTHOR XU Pingya, Aug 12 2017 EXTENSIONS a(0) prepended by Iain Fox, Dec 14 2017 STATUS approved

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Last modified August 22 20:36 EDT 2019. Contains 326186 sequences. (Running on oeis4.)