A252657 Numbers m such that 4^m - m is a semiprime.

2, 11, 17, 33, 55, 59, 63, 153, 315

Offset: 1

Author

Vincenzo Librandi, Dec 20 2014

Keywords

• nonn
• more

Comments

549, 721, and 755 are in the sequence, but not necessarily the next three terms. The other possibilities for a(9) are 483, 503, and 543. - Robert Israel, Feb 10 2019

Examples

			2 is in this sequence because 4^2-2 = 2*7 is semiprime.
17 is in this sequence because 4^17-17 = 6971*2464477 and these two factors are prime.
		

Links

• factordb.com, Status of 4^483-483.

Crossrefs

Cf. A024037 (4^n - n).

Cf. similar sequences listed in A252656.

Programs

Magma

IsSemiprime:=func; [m: m in [2..120] | IsSemiprime(s) where s is 4^m-m];

Mathematica

Select[Range[120], PrimeOmega[4^# - #]==2 &]

Extensions

a(8)-a(9) from Luke March, Jul 08 2015