OFFSET
0,4
COMMENTS
Also column 2 of A181187. - Omar E. Pol, Feb 18 2012
Sum over all partitions of n of the difference between the number of parts and the number of distinct parts. - Alois P. Heinz, Nov 18 2020
LINKS
Alois P. Heinz, Table of n, a(n) for n = 0..1000
FORMULA
a(n) = Sum_{k=1..n} (tau(k)-1)*numbpart(n-k). - Vladeta Jovovic, Jun 26 2004
a(n) ~ exp(Pi*sqrt(2*n/3))*(2*gamma - 2 + log(6*n/Pi^2))/(4*Pi*sqrt(2*n)), where gamma is the Euler-Mascheroni constant A001620. - Vaclav Kotesovec, Oct 24 2016
a(n) = Sum_{i=1..floor(n/2)} A066633(n-i,i). - George Beck, Feb 15 2020
G.f.: Sum_{k>=1} x^(2*k)/(1 - x^k) / Product_{j>=1} (1 - x^j). - Ilya Gutkovskiy, Mar 05 2021
EXAMPLE
The partitions of n=5 are [11111], [1112], [113], [122], [23], [14], [5] and they contain 0 + 1 + 1 + 2 + 2 + 1 + 1 = 8 = A096541(5) parts unequal to 1.
MAPLE
main := proc(n::integer) local a, ndxp, ndxprt, ListOfPartitions, iverbose; with(combinat): ListOfPartitions:=partition(n); a:=0; for ndxp from 1 to nops(ListOfPartitions) do for ndxprt from 1 to nops(ListOfPartitions[ndxp]) do if op(ndxprt, ListOfPartitions[ndxp]) <> 1 then a := a + 1; fi; end do; end do; print("n, a(n):", n, a); end proc;
# second Maple program:
b:= proc(n, i) option remember; local f, g;
if n=0 or i=1 then [1, 0]
else f:= b(n, i-1); g:= `if`(i>n, [0, 0], b(n-i, i));
[f[1]+g[1], f[2]+g[2]+g[1]]
fi
end:
a:= n-> b(n, n)[2]:
seq(a(n), n=0..60); # Alois P. Heinz, Apr 04 2012
MATHEMATICA
f[n_] := Block[{l = Sort[ Flatten[ IntegerPartitions[n]]]}, Length[l] - Count[l, 1]]; Table[ f[n], {n, 0, 20}] (* Robert G. Wilson v, Jun 30 2004 *)
a[n_] := Sum[(DivisorSigma[0, k] - 1)*PartitionsP[n - k], {k, 1, n}]; Table[a[n], {n, 0, 42}] (* Jean-François Alcover, Jan 14 2013, after Vladeta Jovovic *)
PROG
(PARI) a(n)=sum(k=1, n, (numdiv(k)-1)*numbpart(n-k)) \\ Charles R Greathouse IV, Jan 14 2013
CROSSREFS
KEYWORD
nonn
AUTHOR
Thomas Wieder, Jun 24 2004
EXTENSIONS
More terms from Robert G. Wilson v, Jun 30 2004
STATUS
approved