A155589 a(n) = 6^n + 2^n - 1.
1, 7, 39, 223, 1311, 7807, 46719, 280063, 1679871, 10078207, 60467199, 362799103, 2176786431, 13060702207, 78364180479, 470185017343, 2821109972991, 16926659575807, 101559956930559, 609359740534783, 3656158441111551, 21936950642475007, 131621703846461439
Offset: 0
Links
- Paolo Xausa, Table of n, a(n) for n = 0..1000
- Index entries for linear recurrences with constant coefficients, signature (9,-20,12).
Programs
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Mathematica
Table[6^n + 2^n - 1, {n, 0, 25}] (* Paolo Xausa, Jul 30 2024 *) -
PARI
a(n)=6^n+2^n-1 \\ Charles R Greathouse IV, Jun 11 2015
Formula
G.f.: 1/(1-6*x)+1/(1-2*x)-1/(1-x).
E.g.f.: exp(6*x)+exp(2*x)-exp(x).
a(n) = 8*a(n-1)-12*a(n-2)-5 with a(0) = 1, a(1) = 7. - Vincenzo Librandi, Jul 21 2010