A140745 Smallest prime p such that the Mersenne number A000225(p) = 2^p - 1 has exactly n prime factors (counted with multiplicity).

2, 11, 29, 157, 113, 223, 491, 431, 397

Offset: 1

Author

Lekraj Beedassy, Jul 12 2008

Keywords

• nonn
• more

References

• J.-M. De Koninck, Ces nombres qui nous fascinent, Entry 223, pp 63-4, Ellipse Paris 2008.

Crossrefs

Cf. A000225, A001222, A046051, A136033.

Programs

Mathematica

a[n_]:=Module[{p=0},Until[PrimeOmega[2^Prime[p]-1]==n,p++];Prime[p]];Array[a,6] (* James C. McMahon, Jul 14 2025 *)

PARI

a(n) = forprime(p=2, oo, if(bigomega(2^p-1)==n, return(p))); \\ Jinyuan Wang, Aug 10 2021