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A157560
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Half the number of length n integer sequences with sum zero and sum of squares 1568.
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1
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1, 9, 54, 4730, 384345, 17551611, 639200583, 21540673143, 709364141280, 22449552443395, 690983408959437, 20713553342449344, 594627688939323130, 16245942354519666285, 424430686079103349170, 10684143371864906288080
(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,0,1568)/2.
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CROSSREFS
| Sequence in context: A157539 A205814 A157546 * A157588 A058849 A058852
Adjacent sequences: A157557 A157558 A157559 * A157561 A157562 A157563
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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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