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A339041
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Number of unlabeled connected simple graphs with n edges rooted at two indistinguishable vertices.
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6
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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
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OFFSET
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1,2
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LINKS
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Table of n, a(n) for n=1..25.
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FORMULA
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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.
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PROG
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(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}
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CROSSREFS
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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
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KEYWORD
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nonn
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AUTHOR
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Andrew Howroyd, Nov 20 2020
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STATUS
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approved
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