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A137878
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Perfect squares among 17-gonal numbers A051869(k) = k*(15*k - 13)/2.
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4
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1, 17689, 378225, 4109707449, 87870152041, 954775454112481, 20414169462254569, 221815343046210267025, 4742660677722035990769, 51532584126226886201833161, 1101824413949324675985344641, 11972153009151467313136073526409, 255978051492792346696545201859225
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OFFSET
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1,2
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COMMENTS
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Corresponding square roots sqrt(a(n)) are listed in A137879.
Indices of perfect squares among the 17-gonal numbers A051869(k) = k*(15*k - 13)/2 are listed in A137880. Note that all such indices are also perfect squares, their square roots are listed in A137881(k) = sqrt(A137880(k)).
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LINKS
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FORMULA
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a(n) = a(n-1) + 232322*a(n-2) - 232322*a(n-3) - a(n-4) + a(n-5) for n > 5.
G.f.: x*(1 + 17688*x + 128214*x^2 + 17688*x^3 + x^4) / ((1-x)*(1 - 482*x + x^2)*(1 + 482*x + x^2)).
(End)
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PROG
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(PARI) Vec(x*(1+17688*x+128214*x^2+17688*x^3+x^4)/((1-x)*(1-482*x+x^2)*(1+482*x+x^2)) + O(x^20)) \\ Colin Barker, Jun 19 2016
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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