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A333897 Number of unlabeled loopless multigraphs with 4 nodes of degree n or less. 1
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

LINKS

Table of n, a(n) for n=0..40.

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)

CROSSREFS

Row n=4 of A333893.

Sequence in context: A335970 A212967 A301410 * A316937 A269965 A110158

Adjacent sequences:  A333894 A333895 A333896 * A333898 A333899 A333900

KEYWORD

nonn

AUTHOR

Andrew Howroyd, Apr 08 2020

STATUS

approved

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Last modified November 27 06:49 EST 2021. Contains 349365 sequences. (Running on oeis4.)