A261579 Numbers m such that (4^m + 23) / 3 is prime.

2, 3, 5, 6, 27, 47, 66, 77, 83, 105, 197, 231, 293, 702, 1692, 3021, 6270, 6897, 7733, 14537, 15797, 21083, 21276, 28817, 65430, 111231, 137405, 141017, 185225

Offset: 1

Author

Vincenzo Librandi, Aug 27 2015

Keywords

• nonn
• more

Comments

a(30) > 450,000. - Robert Price, Oct 04 2018

Examples

			2 is in the sequence because (4^2 + 23)/3 = 13 is prime.
3 is in the sequence because (4^3 + 23)/3 = 29 is prime.
		

Crossrefs

Cf. similar sequences listed in A261539.

Programs

Magma

[n: n in [0..1500] | IsPrime((4^n+23) div 3)];

Mathematica

Select[Range[0, 5000], PrimeQ[(4^# + 23)/3] &]

Extensions

a(17)-a(28) from Robert Price, Feb 01 2017

a(29) from Robert Price, Oct 04 2018