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A290838 a(n) = smallest prime p such that 2p - 2n + 1 is prime. 2
2, 2, 3, 5, 5, 7, 7, 13, 11, 11, 11, 13, 13, 19, 17, 17, 17, 19, 19, 37, 23, 23, 23, 29, 29, 31, 29, 29, 29, 31, 31, 37, 37, 41, 37, 37, 37, 43, 41, 41, 41, 43, 43, 61, 47, 47, 47, 53, 53, 67, 53, 53, 53, 59, 59, 61, 59, 59, 59, 61, 61, 67, 67, 71, 67, 67, 67, 73 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,1

COMMENTS

a(n) > n. - Iain Fox, Nov 13 2017

LINKS

Iain Fox, Table of n, a(n) for n = 0..20000

FORMULA

a(-n) = A290839(n+1) - Iain Fox, Dec 14 2017

MATHEMATICA

Table[j=0; found=False; While[!found, j++; found=PrimeQ[2Prime[j]-2n+1] && 2Prime[j]-2n+1>0]; Prime[j], {n, 67}]

(* Second program: *)

Table[SelectFirst[Prime@ Range[n^2], And[# > 0, PrimeQ@ #] &[2 # - 2 n + 1] &], {n, 67}] (* Michael De Vlieger, Aug 14 2017 *)

PROG

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

(PARI) a(n) = forprime(p=n+1, , if(isprime(2*p - 2*n + 1), return(p))) \\ Iain Fox, Nov 13 2017

CROSSREFS

Cf. A005382, A063908, A063909, A063910, A063911, A063912, A063913, A020483, A290839.

Sequence in context: A262463 A151800 A259430 * A056896 A089366 A113827

Adjacent sequences:  A290835 A290836 A290837 * A290839 A290840 A290841

KEYWORD

nonn,easy

AUTHOR

XU Pingya, Aug 11 2017

EXTENSIONS

a(0) prepended by Iain Fox, Dec 14 2017

STATUS

approved

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Last modified July 21 00:49 EDT 2019. Contains 325189 sequences. (Running on oeis4.)