OFFSET
1,2
COMMENTS
a(25) >= 428. - Hugo Pfoertner, Jul 28 2019
EXAMPLE
4 is OK because 3^4 + 4^3 = 81 + 64 = 145 = 5*29 (semiprime).
MATHEMATICA
Select[Range[100], PrimeOmega[3^# + #^3]==2&] (* Vincenzo Librandi, May 21 2014 *)
PROG
(Magma)IsSemiprime:=func< n | &+[ k[2]: k in Factorization(n) ] eq 2 >; [ n: n in [1..95] | IsSemiprime(3^n+n^3)]; // Vincenzo Librandi Dec 16 2010
CROSSREFS
KEYWORD
nonn,more,hard
AUTHOR
Zak Seidov, Feb 22 2006
EXTENSIONS
a(14)-a(23) from Luke March, Jul 27 2015
a(24) from Hugo Pfoertner, Jul 28 2019
STATUS
approved