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 A124522 a(n) = smallest k such that 2nk-1 and 2nk+1 are primes. 13
 2, 1, 1, 9, 3, 1, 3, 12, 1, 3, 9, 3, 12, 15, 1, 6, 3, 2, 6, 6, 1, 15, 3, 4, 3, 6, 2, 48, 6, 1, 21, 3, 3, 15, 6, 1, 27, 3, 4, 3, 15, 5, 12, 15, 2, 9, 3, 2, 9, 6, 1, 3, 60, 1, 6, 24, 2, 3, 9, 2, 129, 12, 7, 9, 15, 5, 12, 27, 1, 3, 9, 3, 42, 45, 1, 90, 3, 2, 66, 21, 5, 63, 27, 16, 6, 6, 2, 12, 24, 1, 6 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Robert Israel, Table of n, a(n) for n = 1..10000 MAPLE isA001359 := proc(n) RETURN( isprime(n) and isprime(n+2)) ; end: A124522 := proc(n) local k; k :=1 ; while true do if isA001359(2*n*k-1) then RETURN(k) ; fi ; k := k+1 ; od ; end: for n from 1 to 60 do printf("%d, ", A124522(n)) ; od ; # R. J. Mathar, Nov 06 2006 MATHEMATICA f[n_] := Block[{k = 1}, While[Nand @@ PrimeQ[{-1, 1} + 2n*k], k++ ]; k]; Table[f[n], {n, 91}] (* Ray Chandler, Nov 16 2006 *) PROG (PARI) {for(n=1, 91, k=1; while(!isprime(2*n*k-1)||!isprime(2*n*k+1), k++); print1(k, ", "))} CROSSREFS Cf. A040040, A045753, A002822, A124065, A124518-A124522, A063983. Sequence in context: A185814 A174553 A167015 * A016540 A132620 A156883 Adjacent sequences: A124519 A124520 A124521 * A124523 A124524 A124525 KEYWORD nonn AUTHOR Artur Jasinski, Nov 04 2006 EXTENSIONS Edited and extended by Klaus Brockhaus and R. J. Mathar, Nov 06 2006 STATUS approved

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Last modified November 28 04:05 EST 2023. Contains 367394 sequences. (Running on oeis4.)