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A157550
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Half the number of length n integer sequences with sum zero and sum of squares 648.
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1
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1, 3, 54, 1830, 68175, 2604105, 72741487, 1575681348, 32584952460, 663445574880, 13119864945495, 250743317040879, 4601891725568592, 80821202263252920, 1358608769903073690, 21985893765384549032, 344851090651019364715
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OFFSET
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2,2
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LINKS
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R. H. Hardin, Table of n, a(n) for n=2..50
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FORMULA
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[cache enabling] count(n,s,ss)->count(n,t,tt) where t=s mod n, q=(t-s)/n, tt=ss+2*q*s+n*q^2; count(n,t,tt)=sum[i^2<=tt]{ count(n-1,t-i,tt-i^2) }. a(n)=count(n,0,648)/2.
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CROSSREFS
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Sequence in context: A222203 A224051 A224304 * A224368 A091826 A091796
Adjacent sequences: A157547 A157548 A157549 * A157551 A157552 A157553
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KEYWORD
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nonn
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AUTHOR
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R. H. Hardin Mar 02 2009
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STATUS
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approved
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