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A157535
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Half the number of length n integer sequences with sum zero and sum of squares 18.
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1
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1, 3, 18, 70, 285, 1533, 7084, 29604, 116385, 419815, 1385142, 4278066, 12678757, 36517950, 102364200, 278451568, 733599079, 1872496417, 4639365470, 11183927650, 26287242751, 60341512253, 135432776524, 297482865100
(list; graph; refs; listen; history; internal format)
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OFFSET
| 2,2
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LINKS
| R. H. Hardin, Table of n, a(n) for n=2..50
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FORMULA
| [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,0,18)/2.
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CROSSREFS
| Sequence in context: A026576 A048899 A107583 * A098522 A174764 A114633
Adjacent sequences: A157532 A157533 A157534 * A157536 A157537 A157538
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KEYWORD
| nonn
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AUTHOR
| R. H. Hardin (rhhardin(AT)att.net) Mar 02 2009
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