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A201157
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y-values in the solution to 5*x^2 - 20 = y^2.
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3
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0, 5, 15, 40, 105, 275, 720, 1885, 4935, 12920, 33825, 88555, 231840, 606965, 1589055, 4160200, 10891545, 28514435, 74651760, 195440845, 511670775, 1339571480, 3507043665, 9181559515, 24037634880, 62931345125, 164756400495, 431337856360, 1129257168585
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OFFSET
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1,2
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COMMENTS
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LINKS
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FORMULA
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a(n) = 3*a(n-1) - a(n-2), n>2.
a(n) = 5*Fibonacci(2*n-2) = Lucas(2*n-1) + Lucas(2*n-3) with Lucas(-1) = -1. - Bruno Berselli, Feb 15 2017
a(n) = Lucas(n)^2 - Lucas(n-2)^2. - Greg Dresden, Apr 15 2022
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EXAMPLE
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15 is in the sequence because 15^2 = 5*7^2 - 20.
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MATHEMATICA
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LinearRecurrence[{3, -1}, {0, 5}, 50]
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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