A242271 Numbers n such that n*8^n+1 is semiprime.

1, 2, 3, 9, 24, 32, 35, 51, 75, 234, 243, 392, 417, 472

Offset: 1

Author

Vincenzo Librandi, May 10 2014

Keywords

• nonn
• more
• hard

Comments

The semiprimes of this form are: 9, 129, 1537, 1207959553, 113336795588871485128705, 2535301200456458802993406410753, ...

a(15) >= 483. - Hugo Pfoertner, Aug 05 2019

Links

• factordb.com, Status of 483*8^483+1.

Crossrefs

Cf. similar sequences listed in A242203.

Cf. A064746, A242178.

Programs

Magma

IsSemiprime:=func; [n: n in [1..80] | IsSemiprime(s) where s is n*8^n+1];

Mathematica

Select[Range[80], PrimeOmega[# 8^# + 1] == 2 &]

Extensions

a(10)-a(14) from Hugo Pfoertner and Daniel Suteu, Aug 05 2019