permcount[v_]:=模[{m=1,s=0,k=0,t},对于[i=1,i<=长度[v],i++,t=v[i]];k=如果[i>1&&t==v[[i-1]],k+1,1];m*=t*k;s+=t];s/m] ;
边[v_]:=和[GCD[v[i]],v[[j]]],{i,2,长度[v]},{j,1,i-1}]+总[#,2]和/@v];
a[n_]:=如果[n<2,0,s=0;Do[s+=permcount[p]*(2^(2*Length[p]+edges[p])),{p,IntegerPartitions[n-2]}];s/(n-2)!];