A156771 - OEIS

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A156771

a(n) = 729*n - 531.

198, 927, 1656, 2385, 3114, 3843, 4572, 5301, 6030, 6759, 7488, 8217, 8946, 9675, 10404, 11133, 11862, 12591, 13320, 14049, 14778, 15507, 16236, 16965, 17694, 18423, 19152, 19881, 20610, 21339, 22068, 22797, 23526, 24255, 24984, 25713

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OFFSET

1,1

COMMENTS

The identity (6561*n^2 - 9558*n + 3482)^2 - (81*n^2 - 118*n + 43)*(729*n - 531)^2 = 1 can be written as A156773(n)^2 - A156677(n)*a(n)^2 = 1.

LINKS

Vincenzo Librandi, Table of n, a(n) for n = 1..10000

Index entries for linear recurrences with constant coefficients, signature (2,-1).

FORMULA

a(n) = 2*a(n-1) - a(n-2).

G.f.: x*(198 + 531*x)/(1-x)^2.

E.g.f.: 9*(59 - (59 - 81*x)*exp(x)). - G. C. Greubel, Jun 19 2021