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 A271999 Halogen sequence: a(n) = A018227(n)-1. 2
 1, 11, 17, 35, 53, 85, 117, 167, 217, 289, 361, 459, 557, 685, 813, 975, 1137, 1337, 1537, 1779, 2021, 2309, 2597, 2935, 3273, 3665, 4057, 4507, 4957, 5469, 5981, 6559, 7137, 7785, 8433, 9155, 9877, 10677, 11477, 12359, 13241, 14209, 15177, 16235, 17293 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Terms from 11 to 117 are the atomic numbers of the elements in group 17 in the periodic table. The elements in this group are also called halogens. LINKS Colin Barker, Table of n, a(n) for n = 1..1000 Index entries for linear recurrences with constant coefficients, signature (2,1,-4,1,2,-1). FORMULA G.f.: x*(1 + 9*x - 6*x^2 - 6*x^3 + 9*x^4 - x^5 - 4*x^6 + 2*x^7) / ((1 - x)^4*(1 + x)^2). a(n) = (1/12)*(2*n^3 + 12*n^2 + 28*n - 12) for n>2 and even. a(n) = (1/12)*(2*n^3 + 12*n^2 + 22*n - 24) for n>2 and odd. a(n) = 2*a(n-1) + a(n-2) - 4*a(n-3) + a(n-4) + 2*a(n-5) - a(n-6) for n>8. (End) PROG (PARI) Vec(x*(1 + 9*x - 6*x^2 - 6*x^3 + 9*x^4 - x^5 - 4*x^6 + 2*x^7) / ((1 - x)^4*(1 + x)^2) + O(x^50)) \\ Colin Barker, Nov 14 2017 CROSSREFS Sequence in context: A086711 A039514 A098797 * A317453 A339247 A317678 Adjacent sequences:  A271996 A271997 A271998 * A272000 A272001 A272002 KEYWORD nonn,easy AUTHOR Natan Arie Consigli, Jul 02 2016 STATUS approved

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Last modified May 14 16:48 EDT 2021. Contains 343898 sequences. (Running on oeis4.)