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A151879 Produced by same formula that gives A000568 (unlabeled tournaments), but with LCM instead of GCD in the exponent. 1
1, 1, 1, 2, 8, 52, 528, 8632, 252928, 15494032, 2050181376, 525675623520, 239430803636224, 189133678584246592, 260786292437892272128, 638374284463941710477184, 2842966981002836533300953088, 23866119110542723640161098330368, 394851495657676102988098496313229312 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,4

LINKS

Andrew Howroyd, Table of n, a(n) for n = 0..50

FORMULA

a(n) = Sum_{j} (1/(Product (k^(j_k) (j_k)!))) * 2^{t_j}, where j runs through all partitions of n into odd parts, say with j_1 parts of size 1, j_3 parts of size 3, etc., and t_j = (1/2)*[ Sum_{r=1..n, s=1..n} j_r j_s lcm(r,s) - Sum_{r} j_r ].

MATHEMATICA

permcount[v_] := Module[{m = 1, s = 0, k = 0, t}, For[i = 1, i <= Length[v], i++, t = v[[i]]; k = If[i > 1 && t == v[[i - 1]], k + 1, 1]; m *= t*k; s += t]; s!/m];

edges[v_] := Sum[Sum[LCM[v[[i]], v[[j]]], {j, 1, i - 1}], {i, 2, Length[v]} ] + Sum[Quotient[v[[i]], 2], {i, 1, Length[v]}];

oddp[v_] := (For[i = 1, i <= Length[v], i++, If[BitAnd[v[[i]], 1] == 0, Return[0]]]; 1);

a[n_] := a[n] = (s = 0; Do[If[oddp[p] == 1, s += permcount[p]*2^edges[p]], {p, IntegerPartitions[n]}]; s/n!); (* Jean-Fran├žois Alcover, Nov 13 2017, after Andrew Howroyd *)

PROG

(PARI)

permcount(v) = {my(m=1, s=0, k=0, t); for(i=1, #v, t=v[i]; k=if(i>1&&t==v[i-1], k+1, 1); m*=t*k; s+=t); s!/m}

edges(v) = {sum(i=2, #v, sum(j=1, i-1, lcm(v[i], v[j]))) + sum(i=1, #v, v[i]\2)}

oddp(v) = {for(i=1, #v, if(bitand(v[i], 1)==0, return(0))); 1}

a(n) = {my(s=0); forpart(p=n, if(oddp(p), s+=permcount(p)*2^(edges(p)))); s/n!} \\ Andrew Howroyd, Feb 29 2020

CROSSREFS

Sequence in context: A323843 A132228 A305004 * A191552 A154828 A349012

Adjacent sequences:  A151876 A151877 A151878 * A151880 A151881 A151882

KEYWORD

nonn

AUTHOR

N. J. A. Sloane, Jul 21 2009

STATUS

approved

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Last modified January 19 15:13 EST 2022. Contains 350466 sequences. (Running on oeis4.)