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Search: id:A158491
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| 19, 79, 179, 319, 499, 719, 979, 1279, 1619, 1999, 2419, 2879, 3379, 3919, 4499, 5119, 5779, 6479, 7219, 7999, 8819, 9679, 10579, 11519, 12499, 13519, 14579, 15679, 16819, 17999, 19219, 20479, 21779, 23119, 24499, 25919, 27379, 28879, 30419
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OFFSET
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1,1
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COMMENT
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If A=[A158490] 100*n.^2-10 (n>0, 90, 390, 890,.,); Y=[A005843] 2*n (n>0, 2, 4, 6,.,); X = [A158491] 20*n^2-1 (n>0, 19, 79, 179, .,), we have, for all terms, Pell's equation X^2-A*Y^2=1. Example: 19^2-90*2^2=1; 79^2-390*4^2=1; 179^2-890*6^2=1.
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LINKS
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Edward Everett Withford, Pell Equation
Vincenzo Librandi, X^2-AY^2=1
Wolfram MathWorld, Pell Equation
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FORMULA
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a(n)=20*n^2-1 (n>0)
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EXAMPLE
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For n=1, a(1)=19; n=2, a(2)=79; n=3, a(3)=179
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CROSSREFS
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Cf. A005843, A158490
Sequence in context: A074822 A139871 A142789 this_sequence A139941 A127270 A053665
Adjacent sequences: A158488 A158489 A158490 this_sequence A158492 A158493 A158494
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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 20 2009
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