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 A103115 a(n) = 6*n*(n-1)-1. 3
 -1, -1, 11, 35, 71, 119, 179, 251, 335, 431, 539, 659, 791, 935, 1091, 1259, 1439, 1631, 1835, 2051, 2279, 2519, 2771, 3035, 3311, 3599, 3899, 4211, 4535, 4871, 5219, 5579, 5951, 6335, 6731, 7139, 7559, 7991, 8435, 8891, 9359, 9839, 10331, 10835, 11351, 11879, 12419 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 COMMENTS Star numbers A003154 minus 2. What A163433 does for a triangle, this sequence is doing for a square but giving one-half the results.  Take a square with vertices n, n+1, n+2, and n+3 and find the sum of the four products of each four vertices times the sum of the other three; at n you have n((n+1)+(n+2)+(n+3)) and so on for the other three vertices.  The result of all four is 12*n^2+36*n+22; half this is 6*n^2+18*n+11 and gives the numbers in this sequence starting with n=0. - J. M. Bergot, May 23 2012 Multiplying a(n) by 16 gives the sum of the convolution with itself of each of the 24 permutations of four consecutive numbers. - J. M. Bergot, May 15 2017 LINKS Vincenzo Librandi, Table of n, a(n) for n = 0..1000 Index entries for linear recurrences with constant coefficients, signature (3,-3,1). FORMULA a(n) = A003154(n)-2. G.f.: (1-2*x-11*x^2)/(x-1)^3. - R. J. Mathar, May 11 2009 (adapted by Vincenzo Librandi, May 16 2017). a(n) = 3*a(n-1)-3*a(n-2)+a(n-3), with a(0)=-1, a(1)=-1, a(2)=11. - Harvey P. Dale, Nov 14 2011 a(n) = (n-2)*(n-1 + n + n+1) + (n-1)*(n + n+1) + n*(n+1), which is applying A000914 to four consecutive numbers. - J. M. Bergot, May 15 2017 Sum_{n>=1} 1/a(n) = tan(sqrt(5/3)*Pi/2)*Pi/(2*sqrt(15)). Amiram Eldar, Aug 20 2022 MATHEMATICA Table[6n(n-1)-1, {n, 0, 50}] (* or *) LinearRecurrence[{3, -3, 1}, {-1, -1, 11}, 50] (* Harvey P. Dale, Nov 14 2011 *) CoefficientList[Series[(1 - 2 x - 11 x^2) / (x - 1)^3, {x, 0, 50}], x] (* Vincenzo Librandi, May 16 2017 *) PROG (Magma) [6*n*(n-1)-1: n in [0..50]]; // Vincenzo Librandi, May 16 2017 (PARI) a(n)=6*n*(n-1)-1 \\ Charles R Greathouse IV, Jun 16 2017 CROSSREFS Cf. A000914, A003154, A163433. Sequence in context: A348845 A233546 A092069 * A003777 A222512 A297539 Adjacent sequences:  A103112 A103113 A103114 * A103116 A103117 A103118 KEYWORD easy,sign AUTHOR Jacob Landon (jacoblandon(AT)aol.com), May 09 2009 EXTENSIONS Edited and extended by R. J. Mathar, May 11 2009 Entries rechecked by N. J. A. Sloane, Jul 18 2009 STATUS approved

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Last modified October 2 17:44 EDT 2022. Contains 357228 sequences. (Running on oeis4.)