A060514 - OEIS

%I #11 Jan 23 2020 03:49:36

%S 1,1,1,1,1,3,0,0,1,6,3,4,0,0,1,1,10,15,20,5,0,5,20,15,10,1,1,15,45,75,

%T 90,96,135,315,510,760,843,765,395,105,15,1,1,21,105,245,525,777,1302,

%U 3045,7455,16275,30135,50190,70805,81690,70605,43239,18774,5880,1330

%N Triangle T(n,k) of series-reduced (or homeomorphically irreducible) labeled graphs with n nodes and k edges, k=0..binomial(n,2).

%D I. P. Goulden and D. M. Jackson, Combinatorial Enumeration, John Wiley and Sons, N.Y., 1983.

%H D. M. Jackson and J. W. Reilly, <a href="https://doi.org/10.1016/0095-8956(75)90090-8">The enumeration of homeomorphically irreducible labeled graphs</a>, J. Combin. Theory, B 19 (1975), 272-286.

%F E.g.f. : (1+x*y)^(-1/2)*exp(x*y/2-x^2*y^2/4)*Sum_{k=0..inf}((1+x)*exp(-x^2*y/(1+x*y)))^binomial(k, 2)*(exp(1/2*x^3*y^2/(1+x*y)))^k*x^k/k!

%e Triangle begins:

%e [1],

%e [1],

%e [1, 1],

%e [1, 3, 0, 0],

%e [1, 6, 3, 4, 0, 0, 1],

%e [1, 10, 15, 20, 5, 0, 5, 20, 15, 10, 1],

%e [1, 15, 45, 75, 90, 96, 135, 315, 510, 760, 843, 765, 395, 105, 15, 1],

%e [1, 21, 105, 245, 525, 777, 1302, 3045, 7455, 16275, 30135, 50190, 70805, 81690, 70605, 43239, 18774, 5880, 1330, 210, 21, 1],

%e ...

%Y Row sums: A003514.

%Y For connected graphs see A331437, A331438.

%K nonn,tabf

%O 0,6

%A _Vladeta Jovovic_, Mar 23 2001