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A093431
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a(n) = Sum_{k=1..n} (lcm(n,n-1,...,n-k+2,n-k+1)/lcm(1,2,...,k)).
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13
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1, 3, 7, 13, 31, 38, 113, 165, 265, 420, 1607, 1004, 3979, 6893, 4205, 8665, 40903, 49558, 315477, 162320, 79179, 269877, 1647123, 937552, 1810091, 8445653, 7791355, 3978237, 33071543, 19578860, 283536169, 327438713, 117635955, 742042966, 154748983, 88779588
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OFFSET
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1,2
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COMMENTS
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LINKS
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MAPLE
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a:= n-> add(ilcm(seq(i, i=n-k+1..n))/ilcm(seq(j, j=1..k)), k=1..n): seq(a(n), n=1..40); # Emeric Deutsch, Jan 30 2006
# second Maple program:
b:= proc(n) option remember; `if`(n=1, 1, ilcm(b(n-1), n)) end:
a:= proc(n) option remember; local k, r, s; r, s:= 0, 1;
for k to n do s:= ilcm(s, n-k+1); r:= r+s/b(k) od; r
end:
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MATHEMATICA
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Table[Sum[(LCM@@(n-Range[0, k-1])/LCM@@Range[k]), {k, n}], {n, 33}] (* Jayanta Basu, May 22 2013 *)
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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