A181484 Numbers k such that no power of 2 can be subtracted from 3^k to make a prime.

36, 40, 66, 124, 162, 170, 179, 182, 184, 198, 206, 212, 214, 230, 262, 288, 302, 356, 358, 368, 393, 402, 406, 448, 456, 468, 493, 546, 586, 666, 676, 683, 686, 690, 702, 718, 724, 738, 752, 760, 785, 844, 854, 862, 866, 870, 882, 884, 888, 904, 918, 980

Offset: 1

Author

Carl R. White, Oct 23 2010

Keywords

• nonn

Comments

Zeros of A181483, -1s of A180303.

Odd terms: 179, 393, 493, 683, 785, 1083, 1161, 1181, 1545, ..., . - Robert G. Wilson v, Oct 25 2010

Crossrefs

Cf. A013604, A014224, A180303, A181483.

Programs

Mathematica

fQ[n_] := Block[{k = 0, lmt = Floor@ Log[2, 3^n] +1, m = 3^n}, While[ k < lmt && !PrimeQ[m - 2^k], k++ ]; k == lmt]; Select[ Range@ 995, fQ] (* Robert G. Wilson v, Oct 25 2010 *)

Extensions

a(30) onwards from Robert G. Wilson v, Oct 25 2010

Name clarified by J. Lowell, Aug 21 2020