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 A329404 Interleave 2*n*(3*n-1), (2*n+1)*(6*n+1) for n >= 0. 1
 0, 1, 4, 21, 20, 65, 48, 133, 88, 225, 140, 341, 204, 481, 280, 645, 368, 833, 468, 1045, 580, 1281, 704, 1541, 840, 1825, 988, 2133, 1148, 2465, 1320, 2821, 1504, 3201, 1700, 3605, 1908, 4033, 2128, 4485, 2360, 4961 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 COMMENTS a(n) + a(n+3) = 21, 21, 69, 69, 153, 153, ... Hexagonal spiral for A026741: .                    33--17--35--18                    /                  16   8--17---9--19                  /   /             \                31  15   5---3---7  10                /   /   /         \   \              15   7   2   0===1===4==21==>                \   \   \     /   /   /                29  13   3---1   9  11                  \   \         /   /                  14   6--11---5  23                    \             /                    27--13--25--12 . a(n) is the horizontal sequence from 0. LINKS Colin Barker, Table of n, a(n) for n = 0..1000 Index entries for linear recurrences with constant coefficients, signature (0,3,0,-3,0,1). FORMULA a(n) = n * A165355(n-1). From Colin Barker, Nov 13 2019: (Start) G.f.: x*(1 + 4*x + 18*x^2 + 8*x^3 + 5*x^4) / ((1 - x)^3*(1 + x)^3). a(n) = 3*a(n-2) - 3*a(n-4) + a(n-6) for n > 5. a(n) = (1/4)*(-1)*((-3 + (-1)^n)*n*(-2+3*n)). (End) PROG (PARI) concat(0, Vec(x*(1 + 4*x + 18*x^2 + 8*x^3 + 5*x^4) / ((1 - x)^3*(1 + x)^3) + O(x^45))) \\ Colin Barker, Nov 13 2019 CROSSREFS Cf. A005449, A014641, A026741, A033579, A165355. Sequence in context: A202450 A144292 A338421 * A076943 A138228 A303722 Adjacent sequences:  A329401 A329402 A329403 * A329405 A329406 A329407 KEYWORD nonn,easy AUTHOR Paul Curtz, Nov 13 2019 STATUS approved

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Last modified June 22 12:43 EDT 2021. Contains 345380 sequences. (Running on oeis4.)