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A052109
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a(1)=1, a(n)=a(n-a(1))+a(n-a(2))+a(n-a(3))+....a(n-a(n-1)) for n>1, with convention that a(i)=0 for i<=0.
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2
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1, 1, 2, 5, 12, 30, 73, 178, 434, 1058, 2580, 6291, 15341, 37408, 91217, 222427, 542374, 1322546, 3224947, 7863835, 19175478, 46758223, 114017050, 278023561, 677943348, 1653123143, 4031039074, 9829440768, 23968486545, 58445679752, 142516194140, 347516970942
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OFFSET
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1,3
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LINKS
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EXAMPLE
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a(5) = a(4)+a(4)+a(3) = 5+5+2 = 12.
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MATHEMATICA
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a[1] = 1; a[n_ /; n <= 0] = 0; a[n_] := a[n] = Sum[a[n - a[k]], {k, 1, n-1}]; Table[a[n], {n, 1, 32}] (* Jean-François Alcover, Oct 07 2013 *)
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PROG
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(Haskell)
a052109 n = a052109_list !! (n-1)
a052109_list = 1 : f 2 [1] where
f n xs = z : f (n+1) (z:xs) where
z = sum $ map (a052109 . fromInteger) $
dropWhile (<= 0) $ map (n -) xs
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CROSSREFS
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KEYWORD
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easy,nonn,nice
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AUTHOR
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Robert Lozyniak (11(AT)onna.com), Jan 20 2000
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EXTENSIONS
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STATUS
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approved
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