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A242204
Numbers n such that n*4^n+1 is semiprime.
1
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
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.
Sequence in context: A336745 A034591 A047278 * A172209 A107737 A045138
KEYWORD
nonn,more,hard
AUTHOR
Vincenzo Librandi, May 10 2014
EXTENSIONS
a(15)-a(17) from Luke March, Aug 13 2015
STATUS
approved