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1, 3, 7, 16, 40, 116, 395, 1551, 6847, 33290, 175708, 996696, 6031281, 38710303, 262288647, 1868825536, 13955504572, 108907053412, 885935408411, 7495705968467, 65829634763895, 599033379716074, 5638952863115576, 54830878201599424, 549981672834888561
(list;
graph;
refs;
listen;
history;
text;
internal format)
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OFFSET
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0,2
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COMMENTS
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LINKS
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FORMULA
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G.f.: (1/(1 - x)^2) * Sum_{i>=0} x^i / Product_{j=1..i} (1 - j*x). - Ilya Gutkovskiy, Jun 05 2017
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MAPLE
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b:= proc(n) option remember; `if`(n>0, b(n-1), 0)+combinat[bell](n) end:
a:= proc(n) option remember; `if`(n>0, a(n-1), 0)+b(n) end:
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MATHEMATICA
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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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