A114973 Numbers n such that 5^n + n^5 is a semiprime.

1, 2, 4, 6, 8, 9, 84, 288, 628

Offset: 1

Author

Zak Seidov, Feb 22 2006

Keywords

• nonn
• more
• hard

Comments

a(10) >= 868. - Hugo Pfoertner, Jul 28 2019

Examples

			2 is OK because 5^2 + 2^5 = 25 + 32 = 57 = 3*19 (semiprime).
		

Links

• Status of 5^868-868^5 in factordb.com.

Crossrefs

Cf. A094133, A114970, A114971, A114974.

Programs

Magma

IsSemiprime:=func< n|&+[k[2]: k in Factorization(n)] eq 2 >; [n: n in [1..85]|IsSemiprime(5^n+n^5)]; // Vincenzo Librandi, Dec 16 2010

Mathematica

Select[Range[100],PrimeOmega[5^# + #^5]==2&] (* Vincenzo Librandi, May 21 2014 *)

Extensions

a(8), a(9) from Hugo Pfoertner, Jul 28 2019