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A134957 Number of hyperforests with n unlabeled vertices: analog of A134955 when edges of size 1 are allowed (with no two equal edges). 19
1, 2, 6, 20, 75, 310, 1422, 7094, 37877, 213610, 1256422, 7641700, 47735075, 304766742, 1981348605, 13079643892, 87480944764, 591771554768, 4042991170169, 27864757592632, 193549452132550, 1353816898675732, 9529263306483357, 67457934248821368, 480019516988969011 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

LINKS

Andrew Howroyd, Table of n, a(n) for n = 0..200

FORMULA

Euler transform of A134959. - Gus Wiseman, May 20 2018

EXAMPLE

From Gus Wiseman, May 20 2018: (Start)

Non-isomorphic representatives of the a(3) = 20 hyperforests are the following:

  {}

  {{1}}

  {{1,2}}

  {{1,2,3}}

  {{1},{2}}

  {{1},{2,3}}

  {{2},{1,2}}

  {{3},{1,2,3}}

  {{1,3},{2,3}}

  {{1},{2},{3}}

  {{1},{2},{1,2}}

  {{1},{3},{2,3}}

  {{2},{3},{1,2,3}}

  {{2},{1,3},{2,3}}

  {{3},{1,3},{2,3}}

  {{1,2},{1,3},{2,3}}

  {{1},{2},{3},{2,3}}

  {{1},{2},{3},{1,2,3}}

  {{1},{2},{1,3},{2,3}}

  {{2},{3},{1,3},{2,3}}

  {{3},{1,2},{1,3},{2,3}}

  {{1},{2},{3},{1,3},{2,3}}

  {{2},{3},{1,2},{1,3},{2,3}}

  {{1},{2},{3},{1,2},{1,3},{2,3}}

(End)

MATHEMATICA

etr[p_] := Module[{b}, b[n_] := b[n] = If[n == 0, 1, Sum[Sum[d*p[d], {d, Divisors[j]}]*b[n - j], {j, 1, n}]/n]; b];

EulerT[v_List] := With[{q = etr[v[[#]]&]}, q /@ Range[Length[v]]];

ser[v_] := Sum[v[[i]] x^(i - 1), {i, 1, Length[v]}] + O[x]^Length[v];

b[n_] := Module[{v = {1}}, For[i = 2, i <= n, i++, v = Join[{1}, EulerT[EulerT[2 v]]]]; v];

seq[n_] := Module[{u = 2 b[n]}, Join[{1}, EulerT[ser[EulerT[u]]*(1 - x*ser[u]) + O[x]^n // CoefficientList[#, x]&]]];

seq[24] (* Jean-Fran├žois Alcover, Feb 10 2020, after Andrew Howroyd *)

PROG

(PARI) \\ here b(n) is A318494 as vector

EulerT(v)={Vec(exp(x*Ser(dirmul(v, vector(#v, n, 1/n))))-1, -#v)}

b(n)={my(v=[1]); for(i=2, n, v=concat([1], EulerT(EulerT(2*v)))); v}

seq(n)={my(u=2*b(n)); concat([1], EulerT(Vec(Ser(EulerT(u))*(1-x*Ser(u)))))} \\ Andrew Howroyd, Aug 27 2018

CROSSREFS

Cf. A030019, A035053, A048143, A054921, A134955, A134957, A134959, A144959, A304867, A304911.

Sequence in context: A150167 A150168 A145870 * A052889 A263901 A150169

Adjacent sequences:  A134954 A134955 A134956 * A134958 A134959 A134960

KEYWORD

nonn

AUTHOR

Don Knuth, Jan 26 2008

EXTENSIONS

Terms a(7) and beyond from Andrew Howroyd, Aug 27 2018

STATUS

approved

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Last modified April 11 22:01 EDT 2021. Contains 342888 sequences. (Running on oeis4.)