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
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
KEYWORD
nonn,more,hard
AUTHOR
Vincenzo Librandi, May 10 2014
EXTENSIONS
a(15)-a(17) from Luke March, Aug 13 2015
STATUS
approved