A037034 Least k such that 4*n*k-1 is a prime.

1, 1, 1, 2, 1, 1, 3, 1, 2, 2, 1, 1, 2, 3, 1, 2, 1, 1, 2, 1, 1, 3, 4, 2, 2, 1, 1, 2, 3, 2, 5, 1, 1, 2, 1, 3, 3, 1, 2, 3, 1, 1, 5, 7, 1, 2, 3, 1, 3, 1, 5, 5, 1, 2, 2, 1, 1, 2, 13, 1, 2, 3, 1, 5, 4, 1, 6, 1, 3, 3, 1, 3, 5, 3, 2, 2, 1, 1, 2, 4, 2, 3, 1, 7, 3, 3, 1, 5, 4, 1, 2, 1, 2, 2, 1, 1, 3, 4, 3, 5, 6, 3, 2, 4

Offset: 1

Author

Felice Russo

Keywords

• nonn

Examples

			a(5)=1 because 4*5*1-1=19 is a prime
		

Links

• Harvey P. Dale, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A016014.

Programs

Mathematica

lk[n_]:=Module[{c=4n,k=1},While[!PrimeQ[c*k-1],k++];k]; Array[lk,110] (* Harvey P. Dale, Jun 05 2012 *)

Extensions

More terms from Erich Friedman