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Search: id:A137881
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| 1, 7, 15, 153, 329, 3359, 7223, 73745, 158577, 1619031, 3481471, 35544937, 76433785, 780369583, 1678061799, 17132585889, 36840925793, 376136519975, 808822305647, 8257870853561, 17757249798441, 181297022258367, 389850673260055, 3980276618830513, 8558957561922769
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OFFSET
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1,2
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COMMENT
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A137880 gives the indices m (= a(n)^2) of perfect squares in 17-gonal numbers A051869(m) = m(15m -13)/2. Corresponding 17-gonal numbers are listed in A137878(n) = A051869( a(n)^2 ).
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FORMULA
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a(n) = Sqrt[ A137880(n) ]. A051869( a(n)^2 ) = A137878(n).
For n>=5, a(n) = 22*a(n-2) - a(n-4). [Alekseyev]
a(2n) = (15 - sqrt(30))/30 * (11 + 2*sqrt(30))^n + (15 + sqrt(30))/30 * (11 - 2*sqrt(30))^n. [Alekseyev]
a(2n+1) = (15 + sqrt(30))/30 * (11 + 2*sqrt(30))^n + (15 - sqrt(30))/30 * (11 - 2*sqrt(30))^n. [Alekseyev]
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CROSSREFS
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Cf. A051869 (17-gonal numbers), A137878 (17-gonal numbers that are perfect squares), A137879, A137880.
Sequence in context: A032018 A068366 A156499 this_sequence A042725 A041096 A007541
Adjacent sequences: A137878 A137879 A137880 this_sequence A137882 A137883 A137884
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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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