228863domain: NAppears in sequencesG.f.: (1+x-2*x^2+2*x^3-sqrt(1-2*x-3*x^2+4*x^3-4*x^4))/(2*(1-x+x^2)).at n=18A229734Triangle read by rows where T(n,k) is the number of unlabeled simple graphs covering n vertices with exactly k endpoints (vertices of degree 1).at n=57A327372