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A156772 729n - 198. 3
531, 1260, 1989, 2718, 3447, 4176, 4905, 5634, 6363, 7092, 7821, 8550, 9279, 10008, 10737, 11466, 12195, 12924, 13653, 14382, 15111, 15840, 16569, 17298, 18027, 18756, 19485, 20214, 20943, 21672, 22401, 23130, 23859, 24588, 25317, 26046 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

The identity (6561*n^2-3564*n+485)^2-(81*n^2-44*n+6)*(729*n-198)^2=1 can be written as A156774(n)^2-A156676(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*(531+198*x)/(x-1)^2.

MATHEMATICA

LinearRecurrence[{2, -1}, {531, 1260}, 40]

PROG

(MAGMA) I:=[531, 1260]; [n le 2 select I[n] else 2*Self(n-1)-Self(n-2): n in [1..50]];

(PARI) a(n)=729*n-198 \\ Charles R Greathouse IV, Dec 23 2011

CROSSREFS

Cf. A156774, A156676.

Sequence in context: A174761 A031967 A031521 * A031701 A158367 A225937

Adjacent sequences:  A156769 A156770 A156771 * A156773 A156774 A156775

KEYWORD

nonn,easy

AUTHOR

Vincenzo Librandi, Feb 15 2009

STATUS

approved

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Last modified July 5 20:21 EDT 2020. Contains 335473 sequences. (Running on oeis4.)