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A157515 a(n) = 1000*n - 20. 3
980, 1980, 2980, 3980, 4980, 5980, 6980, 7980, 8980, 9980, 10980, 11980, 12980, 13980, 14980, 15980, 16980, 17980, 18980, 19980, 20980, 21980, 22980, 23980, 24980, 25980, 26980, 27980, 28980, 29980, 30980, 31980, 32980, 33980, 34980 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

The identity (5000*n^2 - 200*n + 1)^2 - (25*n^2 - n)*(1000*n - 20)^2 = 1 can be written as A157516(n)^2 - A157514(n)*a(n)^2 = 1 (see also the second part of the comment at A157514). - Vincenzo Librandi, Jan 26 2012

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 (2,-1).

FORMULA

a(n) = 2*a(n-1) - a(n-2). - Vincenzo Librandi, Jan 26 2012

G.f.: x*(980 + 20*x)/(1-x)^2. - Vincenzo Librandi, Jan 26 2012

MATHEMATICA

LinearRecurrence[{2, -1}, {980, 1980}, 50] (* Vincenzo Librandi, Jan 26 2012 *)

PROG

(MAGMA) I:=[980, 1980]; [n le 2 select I[n] else 2*Self(n-1)-Self(n-2): n in [1..50]]; // Vincenzo Librandi, Jan 26 2012

(PARI) for(n=1, 22, print1(1000*n - 20", ")); \\ Vincenzo Librandi, Jan 26 2012

CROSSREFS

Cf. A157514, A157516.

Sequence in context: A327825 A108904 A091080 * A188337 A109120 A128483

Adjacent sequences:  A157512 A157513 A157514 * A157516 A157517 A157518

KEYWORD

nonn,easy

AUTHOR

Vincenzo Librandi, Mar 02 2009

STATUS

approved

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Last modified January 24 04:35 EST 2020. Contains 331183 sequences. (Running on oeis4.)