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Search: id:A157262
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| A157262 |
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a(n)=36*n^2-55*n+21 (n>0) |
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+0
3
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| 2, 55, 180, 377, 646, 987, 1400, 1885, 2442, 3071, 3772, 4545, 5390, 6307, 7296, 8357, 9490, 10695, 11972, 13321, 14742, 16235, 17800, 19437, 21146, 22927, 24780, 26705, 28702, 30771, 32912, 35125, 37410, 39767, 42196, 44697, 47270
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OFFSET
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1,1
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COMMENT
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If A=[A157262] 36*n^2-55*n+21 (2,55,180,...,); Y=[A157263] 1728*n-1320 (408,2136,3864,...,); X=[A157264] 10368*n^2-15840*n+6049 (577,15841,51841,...,) ; , we have for all terms, Pell's equation X^2-A*Y^2=1. Example: 577^2-2*408^2=1; 15841^2-55*2136^2=1; 51841^2-180*3864^2=1; 108577^2-377*5592^2=1.
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LINKS
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Vincenzo Librandi, X^2-AY^2=1
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FORMULA
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a(n)=36*n^2-55*n+21 (n>0)
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EXAMPLE
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For n=1, a(1)=2; n=2, a(2)=55; n=3, a(3)=377; n=4, a(4)=646
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CROSSREFS
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Cf. A157263, A157264
Sequence in context: A117681 A089180 A034013 this_sequence A007975 A109796 A024029
Adjacent sequences: A157259 A157260 A157261 this_sequence A157263 A157264 A157265
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KEYWORD
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nonn
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AUTHOR
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Vincenzo Librandi (vincenzo.librandi(AT)tin.it), Feb 26 2009
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