OFFSET
1,1
EXAMPLE
a(1) = 3 because 6*8 + 1 = 49 = 7*7, which is semiprime.
a(2) = 4 because 13*16 + 1 = 209 = 11*19, which is semiprime.
MAPLE
A268110:=n->`if`(numtheory[bigomega]((2^n-n+1)*2^n+1)=2, n, NULL): seq(A268110(n), n=1..80); # Wesley Ivan Hurt, Jan 30 2016
MATHEMATICA
Select[Range[105], PrimeOmega[(2^# - # + 1) 2^# + 1] == 2 &]
PROG
(Magma) IsSemiprime:=func<i | &+[d[2]: d in Factorization(i)] eq 2>; [n: n in [2..105]| IsSemiprime(s) where s is (2^n-n+1)*2^n+1];
(PARI) lista(nn) = {for(n=1, nn, if(bigomega((2^n-n+1)*2^n+1) == 2, print1(n, ", "))); } \\ Altug Alkan, Feb 07 2016
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Vincenzo Librandi, Jan 30 2016
EXTENSIONS
a(18)-a(19) from Daniel Suteu, Aug 05 2019
a(20)-a(27) from Tyler Busby, Feb 17 2023
STATUS
approved