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A158317
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a(n) = 400*n - 1.
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2
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399, 799, 1199, 1599, 1999, 2399, 2799, 3199, 3599, 3999, 4399, 4799, 5199, 5599, 5999, 6399, 6799, 7199, 7599, 7999, 8399, 8799, 9199, 9599, 9999, 10399, 10799, 11199, 11599, 11999, 12399, 12799, 13199, 13599, 13999, 14399, 14799, 15199
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OFFSET
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1,1
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COMMENTS
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The identity (400*n-1)^2-(400*n^2-2*n)*(20)^2=1 can be written as a(n)^2-A158316(n)*(20)^2 = 1.
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LINKS
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FORMULA
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a(n) = 2*a(n-1)-a(n-2).
G.f.: x*(399+x)/(1-x)^2.
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MATHEMATICA
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LinearRecurrence[{2, -1}, {399, 799}, 50]
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PROG
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(Magma) I:=[399, 799]; [n le 2 select I[n] else 2*Self(n-1)-Self(n-2): n in [1..50]];
(PARI) a(n) = 400*n - 1.
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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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STATUS
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approved
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