OFFSET
1,1
EXAMPLE
a(1)=7849 because 5^6-6^5=7849=47*167 is a semiprime.
MATHEMATICA
Select[Table[n^(n + 1) - (n + 1)^n, {n, 30}], PrimeOmega[#] == 2&] (* Vincenzo Librandi, Sep 21 2012 *)
PROG
(Magma) IsSemiprime:=func<n | &+[d[2]: d in Factorization(n)] eq 2>; [s: n in [3..30] | IsSemiprime(s) where s is n^(n+1)-(n+1)^n]; // Vincenzo Librandi, Sep 21 2012
CROSSREFS
KEYWORD
nonn
AUTHOR
Hugo Pfoertner, Oct 19 2004
EXTENSIONS
a(9)-a(11) from Vincenzo Librandi, Sep 21 2012
STATUS
approved