

A114974


Numbers n such that 7^n + n^7 is a semiprime.


4




OFFSET

1,1


COMMENTS

627 and 748 are sequence terms < 1100. a(11) >= 510. Unknown factorization also for 622 and 790.  Hugo Pfoertner, Jul 28 2019


LINKS



EXAMPLE

2 is in the sequence because 7^2 + 2^7 = 177 = 3*59 (semiprime).
12 is in the sequence because 7^12 + 12^7 = 13*1067470693 (semiprime). [Vincenzo Librandi, Dec 16 2010]


PROG

(Magma)IsSemiprime:=func<n  &+[k[2]: k in Factorization(n)] eq 2>; [n: n in [1..85]  IsSemiprime(7^n+n^7)] // Vincenzo Librandi, Dec 16 2010


CROSSREFS



KEYWORD

nonn,more,hard


AUTHOR



EXTENSIONS



STATUS

approved



