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 A260040 Triangle read by rows giving numbers H(n,k), number of classes of twin-tree-rooted maps with n edges whose root bond contains k edges. 2
 1, 8, 1, 72, 15, 1, 720, 190, 24, 1, 7780, 2345, 415, 35, 1, 89040, 29127, 6384, 798, 48, 1, 1064644, 367248, 93324, 15162, 1400, 63, 1, 13173216, 4708344, 1332528, 261708, 32400, 2292, 80, 1, 167522976, 61343667, 18829650, 4271652, 657198, 63690, 3555, 99, 1, 2178520080, 811147590, 265116720, 67358500, 12269312, 1506615, 117040, 5280, 120, 1 (list; table; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS See Mullin (1967) for precise definition. The sequence 1, 8, 72, 720,... in the first column has the same values as in A260039. LINKS Table of n, a(n) for n=1..55. R. C. Mullin, On the average activity of a spanning tree of a rooted map, J. Combin. Theory, 3 (1967), 103-121. R. C. Mullin, On the average activity of a spanning tree of a rooted map, J. Combin. Theory, 3 (1967), 103-121. [Annotated scanned copy] FORMULA (k+1)*T(n,k) = A260039(n,k), n>=1, 0<=k=2. - R. J. Mathar, Jul 22 2015 Conjecture: T(n,n-3)= (n+1)*n*(5*n^2+7*n+6)/12 = 72, 190,.... for n>=3. - R. J. Mathar, Jul 22 2015 EXAMPLE Triangle begins: 1, 8,1, 72,15,1, 720,190,24,1, ... CROSSREFS Row sums are A260041. Sequence in context: A347489 A038279 A075503 * A051379 A143499 A114152 Adjacent sequences: A260037 A260038 A260039 * A260041 A260042 A260043 KEYWORD nonn,tabl AUTHOR N. J. A. Sloane, Jul 22 2015 STATUS approved

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Last modified March 4 02:53 EST 2024. Contains 370522 sequences. (Running on oeis4.)