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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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1
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5, 5577, 6435661, 7426747025, 8570459630997, 9890302987423321, 11413401077026881245, 13171054952586033533217, 15199386001883205670450981, 17540078275118266757666898665
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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COMMENTS
| 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
| D. Alpern, Quadratic two integer variable equation solver
Index to sequences with linear recurrences with constant coefficients, signature (1155,-1155,1)
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FORMULA
| 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)
G.f. -x*(5-198*x+x^2) / ( (x-1)*(x^2-1154*x+1) ). - R. J. Mathar, Apr 17 2011
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PROG
| (PARI) vector(20, i, (v=if(i>1, [577, 408; 816, 577]*v-[164; 232], [5; 7]))[1, 1])
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CROSSREFS
| Cf. A000326, A136112-A136118, A135768-A135769, A137693.
Sequence in context: A196627 A013535 A079812 * A202156 A117711 A203689
Adjacent sequences: A137691 A137692 A137693 * A137695 A137696 A137697
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KEYWORD
| easy,nonn
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AUTHOR
| M. F. Hasler (Maximilian.Hasler(AT)gmail.com), Feb 08 2008
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