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Search: id:A137880
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| A137880 |
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Indices n of perfect squares among 17-gonal numbers A051869(n) = n(15n - 13)/2. |
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+0
4
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| 1, 49, 225, 23409, 108241, 11282881, 52171729, 5438325025, 25146664929, 2621261378961, 12120640323841, 1263442546333969, 5842123489426225, 608976686071593889, 2815891401263116401, 293525499243961920321, 1357253813285332678849
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OFFSET
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1,2
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COMMENT
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Corresponding perfect squares are listed in A137878.
Note that all a(n) are perfect squares themselves, their square roots are listed in A137881.
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FORMULA
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A051869( a(n) ) = A137878(n); a(n) = A137881(n)^2.
a(n) = 482*a(n-2) - a(n-4) - 208. [Alekseyev]
a(2n) = ( (15 - sqrt(30))/30 * (11 + 2*sqrt(30))^n + (15 + sqrt(30))/30 * (11 - 2*sqrt(30))^n )^2. [Alekseyev]
a(2n+1) = ( (15 + sqrt(30))/30 * (11 + 2*sqrt(30))^n + (15 - sqrt(30))/30 * (11 - 2*sqrt(30))^n )^2. [Alekseyev]
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CROSSREFS
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Cf. A051869 (17-gonal numbers), A137878 (17-gonal numbers that are perfect squares), A137879, A137881.
Sequence in context: A157919 A100453 A017150 this_sequence A017246 A020274 A158248
Adjacent sequences: A137877 A137878 A137879 this_sequence A137881 A137882 A137883
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KEYWORD
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nonn
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AUTHOR
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Alexander Adamchuk (alex(AT)kolmogorov.com), Feb 19 2008
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EXTENSIONS
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Edited and extended by Max Alekseyev (maxale(AT)gmail.com), Oct 19 2008
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