A333897 - OEIS

%I #6 Apr 10 2020 14:44:28

%S 1,3,10,26,61,128,254,467,821,1376,2224,3470,5269,7785,11254,15930,

%T 22149,30276,40786,54177,71089,92198,118336,150386,189425,236573,

%U 293186,360680,440725,535070,645766,774933,925045,1098666,1298736,1528308,1790869,2090007,2429806,2814476,3248749

%N Number of unlabeled loopless multigraphs with 4 nodes of degree n or less.

%F Conjectures from _Colin Barker_, Apr 10 2020: (Start)

%F G.f.: (1 + x + x^2 + x^3 + x^4)*(1 + x^2 + 2*x^3 + x^4 + x^6) / ((1 - x)^7*(1 + x)^3*(1 + x + x^2)^2).

%F a(n) = 2*a(n-1) + 2*a(n-2) - 4*a(n-3) - 4*a(n-4) + 2*a(n-5) + 9*a(n-6) - 9*a(n-8) - 2*a(n-9) + 4*a(n-10) + 4*a(n-11) - 2*a(n-12) - 2*a(n-13) + a(n-14) for n>13.

%F (End)

%Y Row n=4 of A333893.

%K nonn

%O 0,2

%A _Andrew Howroyd_, Apr 08 2020