A166458 - OEIS

A166458

Numbers k such that 10*k - (-1)^k is prime.

1, 2, 3, 6, 7, 8, 13, 14, 15, 18, 19, 20, 21, 24, 25, 27, 31, 33, 36, 38, 42, 43, 44, 48, 49, 50, 57, 60, 62, 63, 66, 69, 72, 74, 75, 81, 84, 86, 91, 92, 97, 99, 102, 103, 104, 105, 109, 115, 117, 123, 126, 128, 129, 132, 140, 144, 145, 146, 147, 150, 151, 153, 156, 157

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,2

LINKS

G. C. Greubel, Table of n, a(n) for n = 1..10000

EXAMPLE

1*10 - (-1)^1 = 11 is prime, so 1 is a term;

2*10 - (-1)^2 = 19 is prime, so 2 is a term;

3*10 - (-1)^3 = 31 is prime, so 3 is a term;

4*10 - (-1)^4 = 39 = 3*13, so 4 is not a term.

MATHEMATICA

Select[If[PrimeQ[10*# - (-1)^#], #] & /@ Range[6!], IntegerQ] (* G. C. Greubel, May 15 2016 *)