A252661 Numbers m such that 8^m - m is a semiprime.

2, 7, 9, 111, 129, 133, 361

Offset: 1

Author

Vincenzo Librandi, Dec 21 2014

Keywords

• nonn
• more
• hard

Comments

a(8) >= 369. - Hugo Pfoertner, Aug 03 2019

Examples

			2 is in this sequence because 8^2-2 = 2*31 is semiprime.
9 is in this sequence because 8^9-9 = 23*5835553 and these two factors are prime.
		

Links

• factordb.com, Status of 8^369-369.

Crossrefs

Cf. similar sequences listed in A252656.

Programs

Magma

IsSemiprime:=func; [m: m in [1..70] | IsSemiprime(s) where s is 8^m-m];

Mathematica

Select[Range[70],PrimeOmega[8^# - #]==2 &]

Extensions

a(4)-a(7) from Hugo Pfoertner, Aug 03 2019