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 A254285 Hexagonal numbers (A000384) which are also centered triangular numbers (A005448). 3
 1, 1891, 26335, 71156485, 991081981, 2677903145191, 37298379237211, 100780206894952201, 1403687203222107385, 3792762303606727977835, 52826364168762410080471, 142736816433155393822880781, 1988067387723517337746328821, 5371757345852607787523567324911 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS Colin Barker, Table of n, a(n) for n = 1..437 Index entries for linear recurrences with constant coefficients, signature (1,37634,-37634,-1,1). FORMULA a(n) = a(n-1)+37634*a(n-2)-37634*a(n-3)-a(n-4)+a(n-5). G.f.: -x*(x^4+1890*x^3-13190*x^2+1890*x+1) / ((x-1)*(x^2-194*x+1)*(x^2+194*x+1)). EXAMPLE 1891 is in the sequence because it is the 31st hexagonal number and the 36th centered triangular number. PROG (PARI) Vec(-x*(x^4+1890*x^3-13190*x^2+1890*x+1)/((x-1)*(x^2-194*x+1)*(x^2+194*x+1)) + O(x^100)) CROSSREFS Cf. A000384, A005448, A254283, A254284. Sequence in context: A151773 A020321 A177086 * A035869 A045198 A020417 Adjacent sequences: A254282 A254283 A254284 * A254286 A254287 A254288 KEYWORD nonn,easy AUTHOR Colin Barker, Jan 28 2015 STATUS approved

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Last modified May 26 12:53 EDT 2024. Contains 372826 sequences. (Running on oeis4.)