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A091356
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Number of planar partitions of n with exactly 2 rows.
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5
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1, 2, 5, 9, 18, 30, 53, 85, 139, 215, 336, 504, 760, 1115, 1635, 2351, 3375, 4770, 6725, 9368, 13006, 17885, 24510, 33319, 45139, 60743, 81457, 108610, 144334, 190844, 251542, 330082, 431825, 562710, 731154, 946644, 1222305, 1573155, 2019471
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OFFSET
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2,2
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LINKS
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FORMULA
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MAPLE
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b:= proc(n, k) option remember; `if`(n=0, 1, add(add(min(d, k)
*d, d=numtheory[divisors](j))*b(n-j, k), j=1..n)/n)
end:
a:= n-> b(n, 2)-b(n, 1):
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MATHEMATICA
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b[n_, k_] := b[n, k] = If[n == 0, 1, Sum[Sum[Min[d, k] d, {d, Divisors[j]}] b[n - j, k], {j, 1, n}]/n];
a[n_] := b[n, 2] - b[n, 1];
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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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