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A158445 25n^2 + 5. 2
30, 105, 230, 405, 630, 905, 1230, 1605, 2030, 2505, 3030, 3605, 4230, 4905, 5630, 6405, 7230, 8105, 9030, 10005, 11030, 12105, 13230, 14405, 15630, 16905, 18230, 19605, 21030, 22505, 24030, 25605, 27230, 28905, 30630, 32405, 34230, 36105 (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 A158187(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*(6+3*x+x^2)/(1-x)^3.

MATHEMATICA

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

PROG

(MAGMA) I:=[30, 105, 230]; [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, A158187.

Sequence in context: A316362 A081370 A257891 * A046301 A193873 A266955

Adjacent sequences:  A158442 A158443 A158444 * A158446 A158447 A158448

KEYWORD

nonn,easy

AUTHOR

Vincenzo Librandi, Mar 19 2009

STATUS

approved

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Last modified October 16 03:23 EDT 2019. Contains 328038 sequences. (Running on oeis4.)