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 A215851 Number of simple labeled graphs on n nodes with exactly 1 connected component that is a tree or a cycle. 3
 1, 1, 4, 19, 137, 1356, 17167, 264664, 4803129, 100181440, 2359762091, 61937322624, 1792399894837, 56697025885696, 1946238657504975, 72058247875111936, 2862433512904759793, 121439708940308299776, 5480390058971655049939, 262144060822550204416000 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 LINKS Alois P. Heinz, Table of n, a(n) for n = 1..150 FORMULA a(1) = a(2) = 1, a(n) = A000272(n) + A001710(n-1) = n^(n-2) + (n-1)!/2 for n>2. EXAMPLE a(3) = 4: .1-2.  .1-2.  .1-2.  .1 2. .|/ .  .|  .  . / .  .|/ . .3...  .3...  .3...  .3... MAPLE a:= n-> `if`(n<3, 1, (n-1)!/2+n^(n-2)): seq(a(n), n=1..25); CROSSREFS Column k=1 of A215861. The unlabeled version is A215981. Cf. A000272, A001710. Sequence in context: A157303 A007788 A259354 * A197920 A208811 A305725 Adjacent sequences:  A215848 A215849 A215850 * A215852 A215853 A215854 KEYWORD nonn AUTHOR Alois P. Heinz, Aug 25 2012 STATUS approved

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Last modified December 7 09:15 EST 2021. Contains 349574 sequences. (Running on oeis4.)