OFFSET
1,4
COMMENTS
Also sum of the sizes of the Durfee squares of all partitions of the head of the last section of n (see A135010).
LINKS
Alois P. Heinz, Table of n, a(n) for n = 1..1000
G. E. Andrews, Partitions and Durfee Dissection
Eric Weisstein's World of Mathematics, Durfee Square
FORMULA
a(n) ~ log(2) * exp(Pi*sqrt(2*n/3)) / (4*n*sqrt(3)). - Vaclav Kotesovec, Jan 03 2019
MAPLE
b:= proc(n, i) option remember; `if`(n=0, 1,
`if`(i<1, 0, b(n, i-1)+`if`(i>n, 0, b(n-i, i))))
end:
g:= proc(n) option remember;
add(add(b(k, d)*b(n-d^2-k, d),
k=0..n-d^2)*d, d=1..floor(sqrt(n)))
end:
a:= n-> g(n)-g(n-1):
seq(a(n), n=1..70); # Alois P. Heinz, Apr 09 2012
MATHEMATICA
b[n_, i_] := b[n, i] = If[n==0, 1, If[i<1, 0, b[n, i-1] + If[i>n, 0, b[n-i, i]]]]; g[n_] := Sum[Sum[b[k, d]*b[n-d^2-k, d], {k, 0, n-d^2}]*d, {d, 1, Sqrt[n]}]; Table[g[n], {n, 0, 70}] // Differences (* Jean-François Alcover, Feb 21 2017, after Alois P. Heinz *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Omar E. Pol, Mar 03 2012
STATUS
approved