A333897 Number of unlabeled loopless multigraphs with 4 nodes of degree n or less.

1, 3, 10, 26, 61, 128, 254, 467, 821, 1376, 2224, 3470, 5269, 7785, 11254, 15930, 22149, 30276, 40786, 54177, 71089, 92198, 118336, 150386, 189425, 236573, 293186, 360680, 440725, 535070, 645766, 774933, 925045, 1098666, 1298736, 1528308, 1790869, 2090007, 2429806, 2814476, 3248749

Offset: 0

Author

Andrew Howroyd, Apr 08 2020

Keywords

• nonn

Crossrefs

Row n=4 of A333893.

Formula

Conjectures from Colin Barker, Apr 10 2020: (Start)

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).

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.

(End)