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 A254711 Pentagonal numbers (A000326) which are also centered square numbers (A001844). 3
 1, 5, 145, 925, 28085, 179401, 5448301, 34802825, 1056942265, 6751568605, 205041351065, 1309769506501, 39776965164301, 254088532692545, 7716526200523285, 49291865572847185, 1496966305936352945, 9562367832599661301, 290403746825451948001 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS Colin Barker, Table of n, a(n) for n = 1..875 Index entries for linear recurrences with constant coefficients, signature (1,194,-194,-1,1). FORMULA a(n) = a(n-1)+194*a(n-2)-194*a(n-3)-a(n-4)+a(n-5). G.f.: -x*(x^4+4*x^3-54*x^2+4*x+1) / ((x-1)*(x^2-14*x+1)*(x^2+14*x+1)). EXAMPLE 145 is in the sequence because it is the 10th pentagonal number and the 9th centered square number. PROG (PARI) Vec(-x*(x^4+4*x^3-54*x^2+4*x+1)/((x-1)*(x^2-14*x+1)*(x^2+14*x+1)) + O(x^100)) CROSSREFS Cf. A000326, A001844, A254709, A254710. Sequence in context: A081322 A232986 A322954 * A273920 A076218 A267989 Adjacent sequences: A254708 A254709 A254710 * A254712 A254713 A254714 KEYWORD nonn,easy AUTHOR Colin Barker, Feb 06 2015 STATUS approved

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Last modified May 26 14:42 EDT 2024. Contains 372826 sequences. (Running on oeis4.)