a = vector(2^14 - 1) u = 1 { for (x0=1, oo, my (v=1, x=x0); while (v <= #a, if (a[v]==0, a[v] = x0; while (u <= #a && a[u], print (u " " a[u]); u++; ); ); if (x%2, x = (3*x+1)/2; v = 2*v+1, x = x/2; v=2*v ); ); if (u > #a, break; ); ); } quit