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A259161
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Positive pentagonal numbers (A000326) that are triangular numbers (A000217) divided by 2.
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3
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5, 48510, 465793515, 4472549283020, 42945417749765025, 412361896760694487530, 3959498889750770719498535, 38019107927025003687930446040, 365059470355795195660737423378045, 3505300996337237541709397051345542550, 33657899801770684519698434826282476187555
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OFFSET
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1,1
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LINKS
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Colin Barker, Table of n, a(n) for n = 1..251
Index entries for linear recurrences with constant coefficients, signature (9603,-9603,1).
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FORMULA
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G.f.: -5*x*(99*x+1) / ((x-1)*(x^2-9602*x+1)).
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EXAMPLE
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5 is in the sequence because 5 is the 2nd pentagonal number, and 2*5 is the 4th triangular number.
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MATHEMATICA
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LinearRecurrence[{9603, -9603, 1}, {5, 48510, 465793515}, 20] (* Vincenzo Librandi, Jun 20 2015 *)
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PROG
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(PARI) Vec(-5*x*(99*x+1)/((x-1)*(x^2-9602*x+1)) + O(x^20))
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CROSSREFS
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Cf. A000217, A000326, A074378, A259156-A259160, A259162-A259167.
Sequence in context: A307492 A165711 A167369 * A242833 A242478 A247845
Adjacent sequences: A259158 A259159 A259160 * A259162 A259163 A259164
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KEYWORD
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nonn,easy
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AUTHOR
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Colin Barker, Jun 19 2015
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STATUS
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approved
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