A219046 Numbers k such that 3^k + 28 is prime.

1, 2, 4, 5, 6, 10, 14, 16, 25, 50, 54, 66, 76, 109, 124, 129, 154, 201, 210, 225, 324, 844, 1444, 2529, 3029, 3292, 3340, 9162, 44721, 45662, 114085, 197542

Offset: 1

Author

Nicolas M. Perrault, Nov 10 2012

Keywords

• nonn
• more

Comments

a(33) > 2*10^5. - Robert Price, Nov 12 2013

Examples

			3^2 + 28 = 37 and 37 is prime, so 2 is a term.
		

Crossrefs

Cf. Sequences of numbers k such that 3^k + m is prime:

(m = 2) A051783, (m = -2) A014224, (m = 4) A058958, (m = -4) A058959,

(m = 8) A217136, (m = -8) A217135, (m = 10) A217137, (m = -10) A217347,

(m = 14) A219035, (m = -14) A219038, (m = 16) A205647, (m = -16) A219039,

(m = 20) A219040, (m = -20) A219041, (m = 22) A219042, (m = -22) A219043,

(m = 26) A219044, (m = -26) A219045, (m = 28) A219046, (m = -28) A219047,

(m = 32) A219048, (m = -32) A219049, (m = 34) A219050, (m = -34) A219051. Note that if m is a multiple of 3, 3^k + m is also a multiple of 3 (for k greater than 0), and as such isn't prime.

Programs

Mathematica

Do[If[PrimeQ[3^n + 28], Print[n]], {n, 10000}]

PARI

is(n)=isprime(3^n+28) \\ Charles R Greathouse IV, Feb 17 2017

Extensions

a(29)-a(32) from Robert Price, Nov 12 2013