OFFSET
0,2
COMMENTS
a(n) is the number of partitions of the integer 2n+4 into at most n+2 summands each of which is at most n+2. - Geoffrey Critzer, Sep 27 2013
LINKS
Alois P. Heinz, Table of n, a(n) for n = 0..1000
P. Flajolet and R. Sedgewick, Analytic Combinatorics, 2009, page 45.
Shishuo Fu and James Sellers, Enumeration of the degree sequences of line-Hamiltonian multigraphs, INTEGERS 12 (2012), #A24. - From N. J. A. Sloane, Feb 04 2013
FORMULA
a(n) = A000041(2*n+4) - 2*Sum_{k=0..n+1} A000041(k), where A000041(n) = number of partitions of n, due to a formula given in the Fu and Sellers paper. - Paul D. Hanna, Feb 06 2013
EXAMPLE
a(2) = 8 because we have: 4+4 = 4+3+1 = 4+2+2 = 4+2+1+1 = 3+3+2 = 3+3+1+1 = 3+2+2+1 = 2+2+2+2. - Geoffrey Critzer, Sep 27 2013
MAPLE
with(combinat): p:= numbpart:
s:= proc(n) s(n):= p(n) +`if`(n>0, s(n-1), 0) end:
a:= n-> p(2*n+4) -2*s(n+1):
seq(a(n), n=0..40); # Alois P. Heinz, Sep 27 2013
MATHEMATICA
Table[nn=2n; Coefficient[Series[Product[(1-x^(n+i))/(1-x^i), {i, 1, n}], {x, 0, nn}], x^(2n)], {n, 1, 37}] (* Geoffrey Critzer, Sep 27 2013 *)
PROG
(PARI) {a(n)=polcoeff(prod(j=n+3, 2*n+4, 1-q^j)/prod(j=1, n+2, 1-q^j), 2*n+4, q)}
(PARI) {a(n)=numbpart(2*n+4)-2*sum(k=0, n+1, numbpart(k))} \\ Paul D. Hanna, Feb 06 2013
CROSSREFS
KEYWORD
nonn
AUTHOR
Paul D. Hanna, Mar 10 2007
STATUS
approved