OFFSET
1,1
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 1..14
EXAMPLE
39 = 3*13 = 3^3 + 2^3 + 3 + 1.
MATHEMATICA
f[n_] := Last/@FactorInteger[n] == {1, 1}; Select[Array[3^# + 2^# + # + 1&, 90], f[#] &]
Select[Table[3^n + 2^n + n + 1, {n, 130}], PrimeOmega[#] == 2&] (* Vincenzo Librandi, Sep 21 2012 *)
PROG
(PARI) for(n=1, 1e2, if(bigomega(t=3^n+2^n+n+1)==2, print1(t", "))) \\ Charles R Greathouse IV, Apr 16 2012
(Magma) IsSemiprime:=func<n | &+[d[2]: d in Factorization(n)] eq 2>; [s: n in [2..130] | IsSemiprime(s) where s is 3^n + 2^n + n + 1]; // Vincenzo Librandi, Sep 21 2012
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Vladimir Joseph Stephan Orlovsky, Apr 07 2010
STATUS
approved