OFFSET
1,1
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 1..1000
EXAMPLE
4097 is a member because 4097 = 8^4 + 1 = 17*241.
MATHEMATICA
semiPrimeQ[n_] := Total[FactorInteger[n]][[2]] == 2; Select[ Range[200]^4
+1, semiPrimeQ]
Select[Table[n^4 + 1, {n, 80}], PrimeOmega[#] == 2&] (* Vincenzo Librandi, Sep 22 2012 *)
PROG
(Magma) IsSemiprime:= func<n | &+[d[2]: d in Factorization(n)] eq 2>; [s: n in [1..75] | IsSemiprime(s) where s is n^4 + 1]; // Vincenzo Librandi, Sep 22 2012
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Michel Lagneau, Feb 25 2011
STATUS
approved