A364270 a(n) = 2^^n + 3^^n, where ^^ indicates tetration.

2, 5, 31, 7625597485003

Offset: 0

Author

Marco Ripà, Oct 20 2023

Keywords

• nonn
• base
• hard

Comments

a(4) has 3638334640025 digits and is too large to show here.

a(n) is prime for n = 0, 1, 2, 3, but it is not known if a(4) is prime.

Examples

			For n = 3, a(3) = 2^2^2 + 3^3^3 = 2^4 + 3^27 = 7625597485003.
		

Crossrefs

Cf. A004249, A014221, A014222, A321312.

Programs

Mathematica

nmax=3; NestList[2^#&, 1,nmax]+NestList[3^#&,1,nmax] (* Stefano Spezia, Oct 22 2023 *)

Formula

a(n) = A014221(n) + A014222(n+1).

a(n) = A321312(2,n) + A321312(3,n).