A114971 Numbers n such that 3^n + n^3 is a semiprime.

1, 4, 8, 14, 16, 22, 23, 32, 34, 50, 52, 62, 80, 154, 170, 176, 202, 208, 214, 236, 248, 332, 398, 422

Offset: 1

Author

Zak Seidov, Feb 22 2006

Keywords

• nonn
• more
• hard

Comments

a(25) >= 428. - Hugo Pfoertner, Jul 28 2019

Examples

			4 is OK because 3^4 + 4^3 = 81 + 64 = 145 = 5*29 (semiprime).
		

Links

• Status of 3^428-428^3 in factordb.com.

Crossrefs

Cf. A114970, A114973, A114974.

Programs

Magma

IsSemiprime:=func< n | &+[ k[2]: k in Factorization(n) ] eq 2 >; [ n: n in [1..95] | IsSemiprime(3^n+n^3)]; // Vincenzo Librandi Dec 16 2010

Mathematica

Select[Range[100], PrimeOmega[3^# + #^3]==2&] (* Vincenzo Librandi, May 21 2014 *)

Extensions

a(14)-a(23) from Luke March, Jul 27 2015

a(24) from Hugo Pfoertner, Jul 28 2019