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A156856 2025*n^2 + n. 5
2026, 8102, 18228, 32404, 50630, 72906, 99232, 129608, 164034, 202510, 245036, 291612, 342238, 396914, 455640, 518416, 585242, 656118, 731044, 810020, 893046, 980122, 1071248, 1166424, 1265650, 1368926, 1476252, 1587628, 1703054, 1822530 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

The identity (32805000*n^2+16200*n+1)^2-(2025*n^2+n)* (729000*n+180)^2=1 can be written as A157081(n)^2-a(n)* A156868(n)^2=1.

LINKS

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

Index entries for linear recurrences with constant coefficients, signature (3,-3,1).

FORMULA

a(n) = 3*a(n-1)-3*a(n-2)+a(n-3). G.f.: 2x(1013+1012x)/(1-x)^3. - R. J. Mathar, Mar 09 2009

MATHEMATICA

LinearRecurrence[{3, -3, 1}, {2026, 8102, 18228}, 40]

PROG

(MAGMA) I:=[2026, 8102, 18228]; [n le 3 select I[n] else 3*Self(n-1)-3*Self(n-2)+1*Self(n-3): n in [1..40]];

(PARI) a(n)=n*(45*n+1) \\ Charles R Greathouse IV, Dec 23 2011

CROSSREFS

Cf. A156855, A156868, A157081. A subsequence of A031768.

Sequence in context: A183999 A250811 A031768 * A031633 A031543 A031723

Adjacent sequences:  A156853 A156854 A156855 * A156857 A156858 A156859

KEYWORD

nonn,easy

AUTHOR

Vincenzo Librandi, Feb 17 2009

STATUS

approved

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Last modified July 25 15:34 EDT 2017. Contains 289795 sequences.