A067422 Seventh column of triangle A067417.

1, 9, 189, 3969, 83349, 1750329, 36756909, 771895089, 16209796869, 340405734249, 7148520419229, 150118928803809, 3152497504879989, 66202447602479769, 1390251399652075149, 29195279392693578129

Offset: 0

Author

Wolfdieter Lang, Jan 25 2002

Keywords

• nonn
• easy

Links

• Vincenzo Librandi, Table of n, a(n) for n = 0..700
• Index entries for linear recurrences with constant coefficients, signature (21).

Crossrefs

Cf. A067421 (sixth column), A067423 (eighth column), A009965 (powers of 21).

Programs

Magma

[Ceiling(9*(3*7)^(n-1)): n in [0..20]]; // Vincenzo Librandi, Oct 02 2011

Formula

a(n) = A067417(n+6, 6).

a(n) = 9*(3*7)^(n-1), n >= 1, a(0)=1.

G.f.: (1-12*x)/(1-21*x).