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 A254675 Indices of centered triangular numbers (A005448) which are also heptagonal numbers (A000566). 3
 1, 13, 44, 776, 2697, 48069, 167140, 2979472, 10359953, 184679165, 642149916, 11447128728, 39802934809, 709537301941, 2467139808212, 43979865591584, 152922865174305, 2726042129376237, 9478750500998668, 168970632155735080, 587529608196743081 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Also positive integers y in the solutions to 5*x^2 - 3*y^2 - 3*x + 3*y - 2 = 0, the corresponding values of x being A254674. LINKS Colin Barker, Table of n, a(n) for n = 1..1000 Index entries for linear recurrences with constant coefficients, signature (1,62,-62,-1,1). FORMULA a(n) = a(n-1)+62*a(n-2)-62*a(n-3)-a(n-4)+a(n-5). G.f.: x*(12*x^3+31*x^2-12*x-1) / ((x-1)*(x^2-8*x+1)*(x^2+8*x+1)). EXAMPLE 13 is in the sequence because the 13th centered triangular number is 235, which is also the 10th heptagonal number. PROG (PARI) Vec(x*(12*x^3+31*x^2-12*x-1)/((x-1)*(x^2-8*x+1)*(x^2+8*x+1)) + O(x^100)) CROSSREFS Cf. A000566, A005448, A254674, A254676. Sequence in context: A159742 A098385 A048364 * A141549 A121964 A147208 Adjacent sequences:  A254672 A254673 A254674 * A254676 A254677 A254678 KEYWORD nonn,easy AUTHOR Colin Barker, Feb 05 2015 STATUS approved

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Last modified April 16 10:22 EDT 2021. Contains 343036 sequences. (Running on oeis4.)