A242204 Numbers n such that n*4^n+1 is semiprime.

2, 6, 8, 9, 13, 15, 25, 36, 37, 63, 66, 72, 73, 85, 205, 333, 430

Offset: 1

Author

Vincenzo Librandi, May 10 2014

Keywords

• nonn
• more
• hard

Comments

The semiprimes of this form are: 33, 24577, 524289, 2359297, 872415233, 16106127361, 28147497671065601, 170005193383307227693057, 698910239464707491627009, ...

a(18) >= 547. - Hugo Pfoertner, Aug 05 2019

Links

• factordb.com, Status of 547*4^547+1.

Crossrefs

Cf. similar sequences listed in A242203.

Cf. A007646, A050915.

Programs

Magma

IsSemiprime:=func; [n: n in [1..110] | IsSemiprime(s) where s is n*4^n+1];

Mathematica

Select[Range[120], PrimeOmega[# 4^# + 1] == 2 &]

Extensions

a(15)-a(17) from Luke March, Aug 13 2015