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 A158601 a(n) = 400*n^2 + 20. 2
 20, 420, 1620, 3620, 6420, 10020, 14420, 19620, 25620, 32420, 40020, 48420, 57620, 67620, 78420, 90020, 102420, 115620, 129620, 144420, 160020, 176420, 193620, 211620, 230420, 250020, 270420, 291620, 313620, 336420, 360020, 384420, 409620 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,1 COMMENTS The identity (40*n^2 + 1)^2 - (400*n^2 + 20)*(2*n)^2 = 1 can be written as A158602(n)^2 - a(n)*A005843(n)^2 = 1. LINKS Vincenzo Librandi, Table of n, a(n) for n = 0..10000 Vincenzo Librandi, X^2-AY^2=1 Index entries for linear recurrences with constant coefficients, signature (3,-3,1). FORMULA G.f.: -20*(1 + 18*x + 21*x^2)/(x-1)^3. a(n) = 3*a(n-1) - 3*a(n-2) + a(n-3). MATHEMATICA 400 Range[0, 40]^2+20  (* Harvey P. Dale, Feb 05 2011 *) LinearRecurrence[{3, -3, 1}, {20, 420, 1620}, 50] (* Vincenzo Librandi, Feb 16 2012 *) PROG (MAGMA) I:=[20, 420, 1620]; [n le 3 select I[n] else 3*Self(n-1)-3*Self(n-2)+1*Self(n-3): n in [1..40]]; // Vincenzo Librandi, Feb 16 2012 (PARI) for(n=0, 40, print1(400*n^2 + 20", ")); \\ Vincenzo Librandi, Feb 16 2012 CROSSREFS Cf. A005843, A158602. Sequence in context: A196898 A068772 A230349 * A268738 A215290 A130832 Adjacent sequences:  A158598 A158599 A158600 * A158602 A158603 A158604 KEYWORD nonn,easy AUTHOR Vincenzo Librandi, Mar 22 2009 EXTENSIONS Comment rewritten, formula replaced by R. J. Mathar, Oct 28 2009 STATUS approved

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Last modified January 18 07:12 EST 2019. Contains 319269 sequences. (Running on oeis4.)