#include <bits/stdc++.h>

int main() {
	std::ios::sync_with_stdio(false);
	std::cin.tie(nullptr);
	std::cout.tie(nullptr);
	int n, m;
	std::cin >> n >> m;
	std::vector<std::vector<int>> a(n, std::vector<int>(m));
	std::vector<int> cnt(26);
	int sigma = 0;
	for (int i = 0; i < n; ++i) {
		std::string s;
		std::cin >> s;
		for (int j = 0; j < m; ++j) {
			a[i][j] = s[j] - 'a';
			if (!cnt[s[j] - 'a']) {
				++sigma;
			}
			++cnt[s[j] - 'a'];
		}
	}
	auto solve = [&](int d, auto &pattern) -> bool {
		std::vector<std::vector<int>> covered(n, std::vector<int>(m));
		char c1 = pattern[0], c2 = c1;
		int kp = -1;
		for (int i = 0; i < d; ++i)
			if (pattern[i] != c1) {
				c2 = pattern[i];
				kp = i;
				break;
			}
		if (kp == -1)
			return false;
		auto try_match_row = [&](int i, int j) {
			if (j + d > m)
				return false;
			for (int k = 0; k < d; ++k)
				if (a[i][j + k] != pattern[k] || covered[i][j + k])
					return false;
			for (int k = 0; k < d; ++k)
				covered[i][j + k] = true;
			return true;
		};
		auto try_match_column = [&](int i, int j) {
			if (i + d > n)
				return false;
			for (int k = 0; k < d; ++k)
				if (a[i + k][j] != pattern[k] || covered[i + k][j])
					return false;
			for (int k = 0; k < d; ++k)
				covered[i + k][j] = true;
			return true;
		};
		// O(nm)
		for (int i = 0; i < n; ++i) {
			for (int j = 0; j < m; ++j)
				if (!covered[i][j] && a[i][j] == c1 && !try_match_row(i, j)) {
					if (!try_match_column(i, j)) {
						return false;
					}
				}
			for (int j = 0; j < m; ++j)
				if (!covered[i][j] && a[i][j] != c1) {
					if (!try_match_column(i, j)) {
						return false;
					}
				}
		}
		return true;
	};
	std::vector<int> ret;
	for (int d = 1; d <= std::max(n, m); ++d) 
		if (n % d == 0 || m % d == 0) {
			if (sigma == 1) {
				ret.push_back(d);
				continue;
			}
			int total = n * m / d;
			for (int i = 0; i < 26; ++i)
				if (cnt[i] % total != 0)
					continue;
			std::vector<int> bs(d);
			if (d <= m) {
				for (int i = 0; i < d; ++i)
					bs[i] = a[0][i];
				if (solve(d, bs)) {
					ret.push_back(d);
					continue;
				}
			}
			if (d <= n) {
				for (int i = 0; i < d; ++i)
					bs[i] = a[i][0];
				if (solve(d, bs)) {
					ret.push_back(d);
					continue;
				}
			}
		}
	std::cout << ret.size() << '\n';
	for (int x : ret)
		std::cout << x << " ";
	std::cout << '\n';
}