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 A158443 16n^2 - 4. 3
 12, 60, 140, 252, 396, 572, 780, 1020, 1292, 1596, 1932, 2300, 2700, 3132, 3596, 4092, 4620, 5180, 5772, 6396, 7052, 7740, 8460, 9212, 9996, 10812, 11660, 12540, 13452, 14396, 15372, 16380, 17420, 18492, 19596, 20732, 21900, 23100, 24332, 25596 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS The identity (8*n^2-1)^2-(16*n^2-4) *(2*n)^2=1 can be written as A157914(n)^2-a(n)*A005843(n)^2=1. Sequence found by reading the line from 12, in the direction 12, 60,... in the square spiral whose vertices are the generalized decagonal numbers A074377. - Omar E. Pol, Nov 02 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 (3,-3,1). FORMULA a(n) = 3*a(n-1) -3*a(n-2) +a(n-3). G.f: 4*x*(3+6*x-x^2)/(1-x)^3. MATHEMATICA 16Range[60]^2-4  (* Harvey P. Dale, Mar 18 2011 *) PROG (MAGMA) I:=[12, 60, 140]; [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) = 16*n^2 - 4. CROSSREFS Cf. A157914, A005843. Sequence in context: A120644 A099829 A099830 * A153792 A229616 A321465 Adjacent sequences:  A158440 A158441 A158442 * A158444 A158445 A158446 KEYWORD nonn,easy AUTHOR Vincenzo Librandi, Mar 19 2009 STATUS approved

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Last modified March 23 05:36 EDT 2019. Contains 321422 sequences. (Running on oeis4.)