A152580 a(n) = 7^(2^n) + 2.

9, 51, 2403, 5764803, 33232930569603, 1104427674243920646305299203

Offset: 0

Author

Cino Hilliard, Dec 08 2008

Keywords

• nonn
• easy

Comments

These numbers are divisible by 3. This follows by expanding the binomial (6+1)^(2^n) + 2 to get 6h + 1 + 2 for some h. Therefore 3 divides 7^(2^n) + 2.

Crossrefs

Cf. A165425.

Programs

Maple

A152580:=n->7^(2^n) + 2: seq(A152580(n), n=0..8); # Wesley Ivan Hurt, Jan 22 2017

PARI

g(a,n) = if(a%2,b=2,b=1);for(x=0,n,y=a^(2^x)+b;print1(y","))

PARI

a(n) = 7^(2^n) + 2; \\ Michel Marcus, Jan 24 2017

Formula

a(n) = A165425(n+3) + 2. - R. J. Mathar, Sep 10 2016