A124522 a(n) = smallest k such that 2nk-1 and 2nk+1 are primes.

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

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 *)
skp[n_]:=Module[{k=1}, While[AnyTrue[2n k+{1, -1}, CompositeQ], k++]; k]; Join[{2}, Array[skp, 100, 2]] (* Harvey P. Dale, Mar 30 2024 *)

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