A124492 a(n) = least k such that 2*i*k - 1 is prime for 1 <= i <= n.

2, 2, 2, 3, 3, 77385, 1447110, 1447110, 203937090, 107290072890, 4724240531010, 123618251967210, 1272603355923900, 9089306184994125090

Offset: 1

Author

Artur Jasinski, Nov 04 2006

Keywords

• nonn
• more

Crossrefs

Cf. A006254, A124485-A124491, A071576.

Programs

Mathematica

a[n_] := Block[{k = If[n < 6, 1, 5], s}, s = k; While[! AllTrue[k  2 Range[n] - 1, PrimeQ], k += s]; k]; Array[a, 8] (* Giovanni Resta, Apr 01 2017 *)

Extensions

Corrected and extended by Don Reble, Nov 05 2006

a(12)-a(14) from Giovanni Resta, Apr 01 2017