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 A276916 Subsequence of centered square numbers obtained by adding four triangles from A276914 and a central element, a(n) = 4*A276914(n) + 1. 1
 1, 5, 41, 61, 145, 181, 313, 365, 545, 613, 841, 925, 1201, 1301, 1625, 1741, 2113, 2245, 2665, 2813, 3281, 3445, 3961, 4141, 4705, 4901, 5513, 5725, 6385, 6613, 7321, 7565, 8321, 8581, 9385, 9661, 10513, 10805, 11705, 12013, 12961, 13285, 14281, 14621, 15665 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS All terms of this sequence are centered square numbers. Graphically, each term of the sequence is made of four squares, eight triangles and a central element. a(A220185(n+1)) = A008844(2n) = A079291(4n+1), which is a square of a Pell number. LINKS Daniel Poveda Parrilla, Table of n, a(n) for n = 0..10000 Daniel Poveda Parrilla, Illustration of initial terms Index entries for linear recurrences with constant coefficients, signature (1,2,-2,-1,1). FORMULA a(n) = 4*n*(2*n + (-1)^n) + 1. a(n) = 4*n*(2*n + 1) + 1 for n even. a(n) = 4*n*(2*n - 1) + 1 for n odd. a(n) is sum of two squares; a(n) = k^2 + (k+1)^2 where k = 2n-(n mod 2). - David A. Corneth, Sep 27 2016 From Colin Barker, Sep 27 2016: (Start) a(n) = a(n-1) + 2*a(n-2) - 2*a(n-3) - a(n-4) + a(n-5) for n > 4. G.f.: (1+4*x+34*x^2+12*x^3+13*x^4) / ((1-x)^3*(1+x)^2). (End) MAPLE A276916:=n->4*n*(2*n+(-1)^n)+1: seq(A276916(n), n=0..60); # Wesley Ivan Hurt, Sep 27 2016 MATHEMATICA Table[4 n (2 n + (-1)^n) + 1, {n, 0, 44}] (* or *) CoefficientList[Series[(1 + 4 x + 34 x^2 + 12 x^3 + 13 x^4)/((1 - x)^3*(1 + x)^2), {x, 0, 44}], x] (* Michael De Vlieger, Sep 28 2016 *) PROG (PARI) Vec((1+4*x+34*x^2+12*x^3+13*x^4)/((1-x)^3*(1+x)^2) + O(x^50)) \\ Colin Barker, Sep 27 2016 (MAGMA) [4*n*(2*n+(-1)^n)+1 : n in [0..60]]; // Wesley Ivan Hurt, Sep 27 2016 CROSSREFS Cf. A008844, A079291, A220185, A276914. Sequence in context: A232881 A174054 A106963 * A203018 A199692 A031917 Adjacent sequences:  A276913 A276914 A276915 * A276917 A276918 A276919 KEYWORD nonn,easy AUTHOR Daniel Poveda Parrilla, Sep 27 2016 STATUS approved

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Last modified May 28 13:20 EDT 2020. Contains 334683 sequences. (Running on oeis4.)