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Search: id:A137694
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| A137694 |
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Numbers k such that 6k^2-2k=3n^2-n for some integer n>0. |
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+0
2
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| 5, 5577, 6435661, 7426747025, 8570459630997, 9890302987423321, 11413401077026881245, 13171054952586033533217, 15199386001883205670450981, 17540078275118266757666898665
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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Also indices of pentagonal numbers which are half of some other pentagonal number: see A137693 for more details, comments & links.
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LINKS
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D. Alpern, Quadratic two integer variable equation solver
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FORMULA
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a(n) = f^{2n-2}(5,7)[1], where f(x,y) = (577x + 408y - 164, 816x + 577y - 232)
a(n) = (5,7,1,5,7,1,...) (mod 10)
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PROGRAM
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(PARI) vector(20, i, (v=if(i>1, [577, 408; 816, 577]*v-[164; 232], [5; 7]))[1, 1])
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CROSSREFS
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Cf. A000326, A136112-A136118, A135768-A135769, A137693.
Adjacent sequences: A137691 A137692 A137693 this_sequence A137695 A137696 A137697
Sequence in context: A086896 A072021 A079812 this_sequence A117711 A116140 A067816
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KEYWORD
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easy,nonn
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AUTHOR
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M. F. Hasler (Maximilian.Hasler(AT)gmail.com), Feb 08 2008
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