A129291 a(n) = 1 - 3^(3^n) + 9^(3^n).

7, 703, 387400807, 58149737003032434092905183, 196627050475552913618075908526912116282660024455971729157367165907347241304007

Offset: 0

Author

Alexander Adamchuk, Apr 08 2007

Keywords

• nonn

Comments

a(n) is the ratio of two consecutive base-3 Fermat numbers A129290(n) = 3^(3^n) + 1 = {4, 28, 19684, 7625597484988, ...}.

Crossrefs

Cf. A129290 (3^(3^n) + 1).

Cf. A055777 (3^(3^n)).

Cf. A002061 (central polygonal numbers: n^2 - n + 1).

Programs

Mathematica

Table[1 - 3^3^n + 9^3^n, {n,0,5}]

Formula

a(n) = A002061(3^(3^n)). a(n) = A129290(n+1) / A129290(n).