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 A158056 a(n) = 16*n^2 + 2*n. 2
 18, 68, 150, 264, 410, 588, 798, 1040, 1314, 1620, 1958, 2328, 2730, 3164, 3630, 4128, 4658, 5220, 5814, 6440, 7098, 7788, 8510, 9264, 10050, 10868, 11718, 12600, 13514, 14460, 15438, 16448, 17490, 18564, 19670, 20808, 21978, 23180, 24414, 25680 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS The identity (16*n + 1)^2 - (16*n^2 + 2*n)*4^2 = 1 can be written as A158057(n)^2 - a(n)*4^2 = 1. - Vincenzo Librandi, Feb 09 2012 Sequence found by reading the line from 18, in the direction 18, 68, ... 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 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.: 2*x*(-9 - 7*x)/(x-1)^3. MATHEMATICA LinearRecurrence[{3, -3, 1}, {18, 68, 150}, 50] Table[16n^2+2n, {n, 40}]  (* Harvey P. Dale, Apr 13 2011 *) PROG (MAGMA) I:=[18, 68, 150]; [n le 3 select I[n] else 3*Self(n-1)-3*Self(n-2)+1*Self(n-3): n in [1..50]]; (PARI) a(n) = 16*n^2 + 2*n. CROSSREFS Cf. A158057. Sequence in context: A143859 A063523 A045234 * A304061 A214491 A135470 Adjacent sequences:  A158053 A158054 A158055 * A158057 A158058 A158059 KEYWORD nonn,easy AUTHOR Vincenzo Librandi, Mar 12 2009 STATUS approved

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Last modified April 24 04:00 EDT 2019. Contains 322406 sequences. (Running on oeis4.)