OFFSET
1,1
EXAMPLE
2 is in this sequence because 7^2+2 = 3*17 is semiprime.
6 is in this sequence because 7^6+6 = 5*23531 and these two factors are prime.
MATHEMATICA
Select[Range[600], PrimeOmega[7^# + #]==2 &]
PROG
(Magma) IsSemiprime:=func<i | &+[d[2]: d in Factorization(i)] eq 2>; [m: m in [1..600] | IsSemiprime(s) where s is 7^m+m];
CROSSREFS
KEYWORD
nonn
AUTHOR
Vincenzo Librandi, Dec 25 2014
EXTENSIONS
a(9) from Carl Schildkraut, Aug 14 2015
a(10) from Kevin P. Thompson, Apr 25 2022
a(11) from Charles R Greathouse IV, Apr 25 2022
STATUS
approved