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

1,1

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

Table of n, a(n) for n=1..17.

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

Mathematica

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

Prog

(Magma) IsSemiprime:=func<i | &+[d[2]: d in Factorization(i)] eq 2>; [n: n in [1..110] | IsSemiprime(s) where s is n*4^n+1];

Crossrefs

Cf. similar sequences listed in A242203.

Cf. A007646, A050915.

Sequence in context: A336745 A034591 A047278 * A172209 A107737 A045138

Adjacent sequences: A242201 A242202 A242203 * A242205 A242206 A242207

Keyword

nonn,more,hard

Author

Vincenzo Librandi, May 10 2014

Extensions

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

Status

approved