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A252789
Numbers m such that 4^m + m is a semiprime.
1
7, 19, 39, 43, 87, 135, 147, 177, 223, 255, 403
OFFSET
1,1
COMMENTS
From Kevin P. Thompson, Apr 26 2022: (Start)
a(12) >= 765.
795 and 949 are also terms in this sequence. (End)
EXAMPLE
7 is in this sequence because 4^7+7 = 37*443 and these two factors are prime.
19 is in this sequence because 4^19+19 = 11*24988900633 and these two factors are prime.
MATHEMATICA
Select[Range[130], PrimeOmega[4^# + #]==2 &]
PROG
(Magma) IsSemiprime:=func<i | &+[d[2]: d in Factorization(i)] eq 2>; [m: m in [1..130] | IsSemiprime(s) where s is 4^m+m];
(PARI) main(m)=select(m->bigomega(4^m + m)==2, vector(m, i, i)); \\ Anders Hellström, Aug 14 2015
CROSSREFS
Cf. similar sequences listed in A252788.
Cf. A252657.
Sequence in context: A051937 A119327 A152728 * A099061 A078163 A108766
KEYWORD
nonn,more
AUTHOR
Vincenzo Librandi, Dec 24 2014
EXTENSIONS
a(6)-a(9) from Carl Schildkraut, Aug 14 2015
a(10)-a(11) from Kevin P. Thompson, Apr 26 2022
STATUS
approved