OFFSET
1,3
LINKS
Andrew Howroyd, Table of n, a(n) for n = 1..50
P. J. Cameron, Sequences realized by oligomorphic permutation groups, J. Integ. Seqs. Vol. 3 (2000), #00.1.5.
Nevena Francetić, Sarada Herke, and Ian M. Wanless, Parity of Sets of Mutually Orthogonal Latin Squares, arXiv:1703.04764 [math.CO], 2017. See Section 4.1.
Tadeusz Sozański, Enumeration of weak isomorphism classes of signed graphs, J. Graph Theory 4 (1980), no. 2, 127-144. (Zentralblatt 434 #05059)
Ferenc Szöllosi, The two-distance sets in dimension four, arXiv:1806.07861 [math.MG], 2018. See Table 1.
MATHEMATICA
Needs["Combinatorica`"]; Table[Total[Table[NumberOfGraphs[n, m], {m, 0, Binomial[n, 2], 2}]], {n, 1, 15}] (* Geoffrey Critzer, Oct 20 2012; modified by Harvey P. Dale, Aug 08 2013 *)
PROG
(PARI) a(n)={local(p=vector(n));
my(S=0, J() = sum(j=0, floor((n-1)/2), p[2*j+1]),
I2() = (sum(i=1, n, sum(j=1, n, p[i]*p[j]*gcd(i, j))) - J())/2,
M1() = (abs((p[1]-0)*(p[1]-1)) + sum(j=2, n, if(0!=(j%4), p[j], 0))),
inc()=!forstep(i=n, 1, -1, p[i]<n\i && p[i]++ && return; p[i]=0), t); until(inc(), t=0; for( i=1, n, if( n < t+=i*p[i], until(i++>n, p[i]=n); next(2))); t==n && S+=(if(M1() == 0, 2^I2()/prod(i=1, n, i^p[i]*p[i]!), 0) + 2^I2()/prod(i=1, n, i^p[i]*p[i]!))/2); S} \\ This is a modification of M. F. Hasler's PARI program from A002854. - Petros Hadjicostas, Mar 02 2021
CROSSREFS
KEYWORD
nonn,nice
AUTHOR
EXTENSIONS
More terms from Vladeta Jovovic, Jul 19 2000
Terms a(18) and beyond from Andrew Howroyd, Sep 17 2018
STATUS
approved