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Search: id:A157515
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| 980, 1980, 2980, 3980, 4980, 5980, 6980, 7980, 8980, 9980, 10980, 11980, 12980, 13980, 14980, 15980, 16980, 17980, 18980, 19980, 20980, 21980, 22980, 23980, 24980, 25980, 26980, 27980, 28980, 29980, 30980, 31980, 32980, 33980, 34980
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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If A=[A157514] 25*n.^2-n (24, 98, 222, 396,.,); Y=[A157515] 1000*n-20 (980, 1980,2980..,); X=[A157516] 5000*n^2-200*n+1 (4801, 19601, 44401,.,), we have, for all terms, Pell's equation X^2-A*Y^2=1. Example: 4801^2-24*980^2=1; 19601^2-98*1980^2=1; 44401^2-222*2980^2=1.
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LINKS
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Vincenzo Librandi, X^2-AY^2=1
Wolfram MathWorld, Pell Equation
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FORMULA
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a(n)=1000*n-20 (n>0)
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EXAMPLE
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For n=1, a(1)=980; n^2, a(2)=1980; n=3, a(3)=2980
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CROSSREFS
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Cf. A157514, A157516
Sequence in context: A063052 A108904 A091080 this_sequence A109120 A128483 A056937
Adjacent sequences: A157512 A157513 A157514 this_sequence A157516 A157517 A157518
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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), Mar 02 2009
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