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A318796
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Number of 2n-length words w over an n-ary alphabet {a1, a2, ..., an} such that #(w,a1) >= #(w,a2) >= ... >= #(w,an) >= 1, where #(w,x) counts the letters x in word w.
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2
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1, 1, 10, 180, 6496, 322560, 25098480, 2437475040, 322951749120, 51882551360640, 10494386800934400, 2503138912988313600, 720738068391525381120, 239324670990042333696000, 92995858936970165240064000, 41062460981196018797072640000, 20742554869763399771711348736000
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OFFSET
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0,3
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LINKS
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FORMULA
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EXAMPLE
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a(2) = 10: aaab, aaba, aabb, abaa, abab, abba, baaa, baab, baba, bbaa.
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MAPLE
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b:= proc(n, i, t) option remember;
`if`(t=1, 1/n!, add(b(n-j, j, t-1)/j!, j=i..n/t))
end:
a:= n-> `if`(n=0, 1, (2*n)!*b(2*n, 1, n)):
seq(a(n), n=0..20);
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MATHEMATICA
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b[n_, i_, t_] := b[n, i, t] =
If[t == 1, 1/n!, Sum[b[n-j, j, t-1]/j!, {j, i, n/t}]];
a[n_] := If[n == 0, 1, (2n)! b[2n, 1, n]];
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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