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A195820
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Total number of smallest parts in all partitions of n that do not contain 1 as a part.
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13
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0, 1, 1, 3, 2, 7, 5, 12, 13, 22, 22, 43, 43, 67, 81, 117, 133, 195, 223, 312, 373, 492, 584, 782, 925, 1190, 1433, 1820, 2170, 2748, 3268, 4075, 4872, 5997, 7150, 8781, 10420, 12669, 15055, 18198, 21535, 25925, 30602, 36624, 43201, 51428, 60478, 71802, 84215
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OFFSET
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1,4
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COMMENTS
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Total number of smallest parts in all partitions of the head of the last section of the set of partitions of n.
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LINKS
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FORMULA
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G.f.: Sum_{i>=2} x^i/(1 - x^i) * Product_{j>=i} 1/(1 - x^j). - Ilya Gutkovskiy, Apr 03 2017
a(n) ~ exp(Pi*sqrt(2*n/3)) / (8*sqrt(3)*n) * (1 - (72 + 5*Pi^2)*sqrt(6) / (144*Pi*sqrt(n))). - Vaclav Kotesovec, Jul 31 2017
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EXAMPLE
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For n = 8 the seven partitions of 8 that do not contain 1 as a part are:
. (8)
. (4) + (4)
. 5 + (3)
. 6 + (2)
. 3 + 3 + (2)
. 4 + (2) + (2)
. (2) + (2) + (2) + (2)
Note that in every partition the smallest parts are shown between parentheses. The total number of smallest parts is 1+2+1+1+1+2+4 = 12, so a(8) = 12.
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MAPLE
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b:= proc(n, i) option remember;
`if`(n=0 or i<2, 0, b(n, i-1)+
add(`if`(n=i*j, j, b(n-i*j, i-1)), j=1..n/i))
end:
a:= n-> b(n, n):
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MATHEMATICA
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Table[s = Select[IntegerPartitions[n], ! MemberQ[#, 1] &]; Plus @@ Table[Count[x, Min[x]], {x, s}], {n, 50}] (* T. D. Noe, Oct 19 2011 *)
b[n_, i_] := b[n, i] = If[n==0 || i<2, 0, b[n, i-1] + Sum[If[n== i*j, j, b[n-i*j, i-1]], {j, 1, n/i}]]; a[n_] := b[n, n]; Table[a[n], {n, 1, 60}] (* Jean-François Alcover, Oct 12 2015, after Alois P. Heinz *)
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PROG
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(Sage)
return sum(list(p).count(min(p)) for p in Partitions(n, min_part=2))
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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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