from collections import defaultdict

a = [5, 4, 0, 3, 1, 2, 6]
d = defaultdict(set)
for i in range(len(a)):
    s = set()
    idx = i
    while idx not in s:
        s.add(idx)
        idx = a[idx]
    d[len(s)].add(tuple(s))
res = max(d)
path = d[max(d)]
print(res, path)

(3, set([(0, 2, 5)]))