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A158446 25n^2 - 5. 2
20, 95, 220, 395, 620, 895, 1220, 1595, 2020, 2495, 3020, 3595, 4220, 4895, 5620, 6395, 7220, 8095, 9020, 9995, 11020, 12095, 13220, 14395, 15620, 16895, 18220, 19595, 21020, 22495, 24020, 25595, 27220, 28895, 30620, 32395, 34220, 36095 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

The identity (10*n^2-1)^2-(25*n^2-5)*(2*n)^2=1 can be written as A158447(n)^2-a(n)*A005843(n)^2=1.

LINKS

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

Vincenzo Librandi, X^2-AY^2=1

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: 5*x*(4+7*x-x^2)/(1-x)^3.

MATHEMATICA

Table[25n^2-5, {n, 50}]

LinearRecurrence[{3, -3, 1}, {20, 95, 220}, 40] (* Harvey P. Dale, May 05 2019 *)

PROG

(MAGMA) I:=[20, 95, 220]; [n le 3 select I[n] else 3*Self(n-1)-3*Self(n-2)+Self(n-3): n in [1..50]];

(PARI) a(n) = 25*n^2 - 5.

CROSSREFS

Cf. A005843, A158447.

Sequence in context: A144359 A124948 A126407 * A221704 A222772 A267646

Adjacent sequences:  A158443 A158444 A158445 * A158447 A158448 A158449

KEYWORD

nonn,easy

AUTHOR

Vincenzo Librandi, Mar 19 2009

STATUS

approved

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Last modified August 12 07:10 EDT 2022. Contains 356067 sequences. (Running on oeis4.)