0,2

Similar to unlabeled tournaments (A000586), with the additional feature that each node carries either a plus sign or a minus sign.

Equivalence is defined with respect to the action of S_n on the nodes (and the induced action on the edges).

N. J. A. Sloane, Table of n, a(n) for n = 0..30

a(n) = Sum_{j} (1/(Product (r^(j_r) (j_r)!))) * 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 gcd(r,s) + Sum_{r} j_r ].

with(combinat); with(numtheory);

for n from 1 to 30 do

p:=partition(n); s:=0:

for k from 1 to nops(p) do

# get next partition of n

ex:=1:

# discard if there is an even part

for i from 1 to nops(p[k]) do if p[k][i] mod 2=0 then ex:=0:break:fi: od:

# analyze an odd partition

if ex=1 then

# convert partition to list of sizes of parts

q:=convert(p[k], multiset);

for i from 1 to n do a(i):=0: od:

for i from 1 to nops(q) do a(q[i][1]):=q[i][2]: od:

# get number of parts

nump := add(a(i), i=1..n);

# get multiplicity

c:=1: for i from 1 to n do c:=c*a(i)!*i^a(i): od:

# get exponent t(j)

tj:=0;

for i from 1 to n do for j from 1 to n do

if a(i)>0 and a(j)>0 then tj:=tj+a(i)*a(j)*gcd(i, j); fi;

od: od:

s:=s + (1/c)*2^((tj+nump)/2);

fi:

od;

A[n]:=s;

od:

[seq(A[n], n=1..30)];

Cf. A000568.

Sequence in context: A030888 A030801 A082480 this_sequence A109458 A030963 A030879

Adjacent sequences: A093931 A093932 A093933 this_sequence A093935 A093936 A093937

nonn

Nadia Heninger (nadiah(AT)cs.princeton.edu) and N. J. A. Sloane (njas(AT)research.att.com), Jul 21 2009