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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
OFFSET
0,1
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. A067076 (indices n at which a(n) = 2).
Sequence in context: A195352 A103507 A219252 * A346651 A085694 A258570
KEYWORD
nonn,easy
AUTHOR
XU Pingya, Aug 12 2017
EXTENSIONS
a(0) prepended by Iain Fox, Dec 14 2017
STATUS
approved