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 A254138 Pentagonal numbers (A000326) which are also centered hexagonal numbers (A003215). 3
 1, 7957, 1185037, 10596309577, 1578130224697, 14111253811878301, 2101618114050816901, 18792154258821103289617, 2798754265133491448134897, 25025774916617575492416996517, 3727140237435880812247465267837, 33327174817289665775049786996211801 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS Colin Barker, Table of n, a(n) for n = 1..327 Index entries for linear recurrences with constant coefficients, signature (1,1331714,-1331714,-1,1). FORMULA a(n) = a(n-1)+1331714*a(n-2)-1331714*a(n-3)-a(n-4)+a(n-5). G.f.: -x*(x^4+7956*x^3-154634*x^2+7956*x+1) / ((x-1)*(x^2-1154*x+1)*(x^2+1154*x+1)). EXAMPLE 7957 is in the sequence because it is the 73rd pentagonal number and the 52nd centered hexagonal number. PROG (PARI) Vec(-x*(x^4+7956*x^3-154634*x^2+7956*x+1)/((x-1)*(x^2-1154*x+1)*(x^2+1154*x+1)) + O(x^100)) CROSSREFS Cf. A000326, A003215, A254136, A254137. Sequence in context: A316907 A293623 A316908 * A157660 A236786 A252190 Adjacent sequences:  A254135 A254136 A254137 * A254139 A254140 A254141 KEYWORD nonn,easy AUTHOR Colin Barker, Jan 26 2015 STATUS approved

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Last modified January 27 08:21 EST 2022. Contains 350606 sequences. (Running on oeis4.)