A063681 Primes p such that 2p+7 is a power of three.

37, 265717, 193710241, 1270932914161, 187855106306818130162790081799568953899918191769361, 884821727139988111281341588371104523273965529248966451172919369920848760385637

Offset: 1

Author

Jud McCranie, Jul 29 2001

Keywords

• nonn

Comments

If (3^i-7)/2 is prime then x=3^i-7 is a solution of sigma(x)+7 = sigma(x+7). See A063680 and indices resulting in primes are in A063679.

The next term (a(7)) has 118 digits. - Harvey P. Dale, May 10 2014

Crossrefs

Cf. A063679, A063680.

Programs

Mathematica

Select[(#-7)/2&/@(3^Range[2,250]),PrimeQ] (* Harvey P. Dale, May 10 2014 *)

Formula

2*37+7 = 3^4, so 37 is in the sequence.