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A101180
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Numbers n such that 19*n^2 + 19*n + 1 is a square.
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3
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0, 8, 671, 15639, 42159, 981911, 77624048, 1807894920, 4873553880, 113507005568, 8973184757831, 208989037004319, 563373081435879, 13121182828725551, 1037282211558181688, 24158714697817430640, 65124801462951244560, 1516782492521509296728
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OFFSET
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1,2
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COMMENTS
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Define a(1)=0, a(2)=8, a(3)=671, a(4)=15639, a(5)=42159, a(6)=981911, the first 6 terms found for the sequence then a(7)=57799*(2*a(3)+1)-a(2)-1, a(8)=57799*(2*a(4)+1)-a(1)-1 for n>8 a(n)=57799*(2*a(n-4)+1)-a(n-8)-1 remark:57799 = 38*39*39+1 =2*19*(39^2)+1
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LINKS
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FORMULA
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G.f.: -x^2*(8*x^6+663*x^5+14968*x^4+26520*x^3+14968*x^2+663*x+8) / ((x-1)*(x^4-340*x^2+1)*(x^4+340*x^2+1)). - Colin Barker, Mar 05 2013
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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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