A252662 Numbers m such that 9^m - m is a semiprime.

4, 8, 10, 14, 20, 26, 38, 44, 56, 80, 190

Offset: 1

Author

Vincenzo Librandi, Dec 22 2014

Keywords

• nonn
• more
• hard

Comments

a(12) >= 250. - Hugo Pfoertner, Aug 03 2019

Examples

			4 is in this sequence because 9^4-4 = 79*83 and these two factors are prime.
14 is in this sequence because 9^14-14 = 163*140348419969 and these two factors are prime.
		

Links

• factordb.com, Status of 9^250-250.

Crossrefs

Cf. similar sequences listed in A252656.

Programs

Magma

IsSemiprime:=func; [m: m in [1..80] | IsSemiprime(s) where s is 9^m-m];

Mathematica

Select[Range[80], PrimeOmega[9^# - #]==2 &]

Extensions

a(11) from Hugo Pfoertner, Aug 03 2019