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A156868 729000n + 180. 4
729180, 1458180, 2187180, 2916180, 3645180, 4374180, 5103180, 5832180, 6561180, 7290180, 8019180, 8748180, 9477180, 10206180, 10935180, 11664180, 12393180, 13122180, 13851180, 14580180, 15309180, 16038180, 16767180, 17496180 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

The identity (32805000n^2+16200*n+1)^2-(2025n^2+n)*(729000n+180)^2=1 can be written as A157081(n)^2-A156856(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.  180*x*(4051-x)/(x-1)^2.

MATHEMATICA

LinearRecurrence[{2, -1}, {729180, 1458180}, 40]

729000*Range[30]+180 (* Harvey P. Dale, Jan 11 2014 *)

PROG

(MAGMA) I:=[729180, 1458180]; [n le 2 select I[n] else 2*Self(n-1)-Self(n-2): n in [1..30]];

(PARI) a(n)=729000*n+180 \\ Charles R Greathouse IV, Dec 23 2011

CROSSREFS

Cf. A156867, A156856, A157081.

Sequence in context: A321495 A234495 A156867 * A238297 A236901 A107447

Adjacent sequences:  A156865 A156866 A156867 * A156869 A156870 A156871

KEYWORD

nonn,easy

AUTHOR

Vincenzo Librandi, Feb 17 2009

STATUS

approved

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Last modified April 24 20:29 EDT 2019. Contains 322446 sequences. (Running on oeis4.)