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Search: id:A023856
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| A023856 |
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a(n) = s(1)t(n)+s(2)t(n-1)+...+s(k)t(n+1-k), where k=[ (n+1)/2 ], s = (natural numbers), t = (natural numbers >= 2). |
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+0
3
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| 2, 3, 10, 13, 28, 34, 60, 70, 110, 125, 182, 203, 280, 308, 408, 444, 570, 615, 770, 825, 1012, 1078, 1300, 1378, 1638, 1729, 2030, 2135, 2480, 2600, 2992, 3128, 3570, 3723, 4218, 4389, 4940, 5130, 5740, 5950, 6622, 6853, 7590, 7843, 8648, 8924, 9800, 10100, 11050, 11375
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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Or, a(n) = s(1)s(n) + s(2)s(n-1) + ... + s(k)s(n-k+1), where k = [ n/2 ] and s = (natural numbers).
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FORMULA
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a(n) = (n+2)*[4n^2+13n+6-3(n+2)(-1)^n]/48.
a(n)=sum{k=1..[2*n+1+(-1)^(n+1)]/4, (n-k+1)(k-1)} with n>=3 - Paolo P. Lava (ppl(AT)spl.at), Jan 31 2007
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CROSSREFS
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Sequence in context: A066089 A004688 A024852 this_sequence A129315 A075770 A135101
Adjacent sequences: A023853 A023854 A023855 this_sequence A023857 A023858 A023859
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KEYWORD
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nonn
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AUTHOR
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Clark Kimberling (ck6(AT)evansville.edu)
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