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A259158
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Positive triangular numbers (A000217) that are heptagonal numbers (A000566) divided by 2.
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3
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171, 355817826, 739874066553765, 1538466018777014327028, 3199027777735470191011289295, 6651936797966044301302839516949686, 13831784604089070782667939513452521937961, 28761287297921206463992005998270360082445758120
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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..158
Index entries for linear recurrences with constant coefficients, signature (2079363,-2079363,1).
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FORMULA
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G.f.: -171*x*(1443*x+1) / ((x-1)*(x^2-2079362*x+1)).
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EXAMPLE
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171 is in the sequence because 171 is the 18th triangular number, and 2*171 is the 12th heptagonal number.
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MATHEMATICA
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LinearRecurrence[{2079363, -2079363, 1}, {171, 355817826, 739874066553765}, 20] (* Vincenzo Librandi, Jun 20 2015 *)
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PROG
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(PARI) Vec(-171*x*(1443*x+1) / ((x-1)*(x^2-2079362*x+1)) + O(x^20))
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CROSSREFS
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Cf. A000217, A000566, A259156, A259157, A259159-A259167.
Sequence in context: A097844 A076573 A015356 * A252139 A252132 A252131
Adjacent sequences: A259155 A259156 A259157 * A259159 A259160 A259161
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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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