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A339041 Number of unlabeled connected simple graphs with n edges rooted at two indistinguishable vertices. 6
1, 2, 7, 21, 73, 255, 946, 3618, 14376, 58957, 249555, 1087828, 4878939, 22488282, 106432530, 516783762, 2572324160, 13116137104, 68461594211, 365559412868, 1995532789212, 11129600885183, 63381069498524, 368338847181336, 2183239817036378 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Table of n, a(n) for n=1..25.

FORMULA

G.f.: f(x)/g(x) - (r(x)^2 + r(x^2))/2 where f(x), g(x) and r(x) are the g.f.'s of A339064, A000664 and A339039.

PROG

(PARI) \\ See A339063 for G.

seq(n)={my(A=O(x*x^n), g=G(2*n, x+A, []), gr=G(2*n, x+A, [1])/g); Vec(G(2*n, x+A, [1, 1])/g - gr^2 + G(2*n, x+A, [2])/g - subst(gr, x, x^2))/2}

CROSSREFS

Cf. A000664, A002905, A303831, A303832, A339039, A339040, A339043, A339044, A339063, A339064.

Sequence in context: A330058 A220726 A127540 * A319852 A060900 A305850

Adjacent sequences:  A339038 A339039 A339040 * A339042 A339043 A339044

KEYWORD

nonn

AUTHOR

Andrew Howroyd, Nov 20 2020

STATUS

approved

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Last modified April 14 15:18 EDT 2021. Contains 342949 sequences. (Running on oeis4.)