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Search: id:A158444
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| 20, 68, 148, 260, 404, 580, 788, 1028, 1300, 1604, 1940, 2308, 2708, 3140, 3604, 4100, 4628, 5188, 5780, 6404, 7060, 7748, 8468, 9220, 10004, 10820, 11668, 12548, 13460, 14404, 15380, 16388, 17428, 18500, 19604, 20740, 21908, 23108, 24340, 25604
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OFFSET
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1,1
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COMMENT
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If A=[A158444] 16*n.^2+4 (n>0, 20, 68,148,.,); Y=[A005843] 2*n (n>0, 2, 4, 6,.,); X = [A081585] 8*n^2+1 (n>0, 9, 33, 73, .,), we have, for all terms, Pell's equation X^2-A*Y^2=1. Example: 9^2-20*2^2=1; 33^2-68*4^2=1; 73^2-148*6^2=1.
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LINKS
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Vincenzo Librandi, X^2-AY^2=1
Wolfram MathWorld, Pell Equation
Edward Everett Withford, Pell Equation
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FORMULA
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a(n)=16*n^2+4 (n>0)
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EXAMPLE
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For n=1, a(1)=20; n=2, a(2)=68; n=3, a(3)=148
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CROSSREFS
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Cf, A005843, A081585
Sequence in context: A117432 A033577 A074632 this_sequence A145191 A044158 A044539
Adjacent sequences: A158441 A158442 A158443 this_sequence A158445 A158446 A158447
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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 19 2009
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