#include <bits/stdc++.h>
using namespace std;
using i64 = long long;
template <class T> constexpr T power(T a, i64 b) {
T res = 1;
for (; b; b /= 2, a *= a) {
if (b % 2) {
res *= a;
}
}
return res;
}
constexpr i64 mul(i64 a, i64 b, i64 p) {
i64 res = a * b - i64(1.L * a * b / p) * p;
res %= p;
if (res < 0) {
res += p;
}
return res;
}
template <i64 P> struct MLong {
i64 x;
constexpr MLong() : x{} {}
constexpr MLong(i64 x) : x{norm(x % getMod())} {}
static i64 Mod;
constexpr static i64 getMod() {
if (P > 0) {
return P;
} else {
return Mod;
}
}
constexpr static void setMod(i64 Mod_) { Mod = Mod_; }
constexpr i64 norm(i64 x) const {
if (x < 0) {
x += getMod();
}
if (x >= getMod()) {
x -= getMod();
}
return x;
}
constexpr i64 val() const { return x; }
explicit constexpr operator i64() const { return x; }
constexpr MLong operator-() const {
MLong res;
res.x = norm(getMod() - x);
return res;
}
constexpr MLong inv() const {
assert(x != 0);
return power(*this, getMod() - 2);
}
constexpr MLong &operator*=(MLong rhs) & {
x = mul(x, rhs.x, getMod());
return *this;
}
constexpr MLong &operator+=(MLong rhs) & {
x = norm(x + rhs.x);
return *this;
}
constexpr MLong &operator-=(MLong rhs) & {
x = norm(x - rhs.x);
return *this;
}
constexpr MLong &operator/=(MLong rhs) & { return *this *= rhs.inv(); }
friend constexpr MLong operator*(MLong lhs, MLong rhs) {
MLong res = lhs;
res *= rhs;
return res;
}
friend constexpr MLong operator+(MLong lhs, MLong rhs) {
MLong res = lhs;
res += rhs;
return res;
}
friend constexpr MLong operator-(MLong lhs, MLong rhs) {
MLong res = lhs;
res -= rhs;
return res;
}
friend constexpr MLong operator/(MLong lhs, MLong rhs) {
MLong res = lhs;
res /= rhs;
return res;
}
friend constexpr std::istream &operator>>(std::istream &is, MLong &a) {
i64 v;
is >> v;
a = MLong(v);
return is;
}
friend constexpr std::ostream &operator<<(std::ostream &os,
const MLong &a) {
return os << a.val();
}
friend constexpr bool operator==(MLong lhs, MLong rhs) {
return lhs.val() == rhs.val();
}
friend constexpr bool operator!=(MLong lhs, MLong rhs) {
return lhs.val() != rhs.val();
}
};
template <> i64 MLong<0LL>::Mod = i64(1E18) + 9;
template <int P> struct MInt {
int x;
constexpr MInt() : x{} {}
constexpr MInt(i64 x) : x{norm(x % getMod())} {}
static int Mod;
constexpr static int getMod() {
if (P > 0) {
return P;
} else {
return Mod;
}
}
constexpr static void setMod(int Mod_) { Mod = Mod_; }
constexpr int norm(int x) const {
if (x < 0) {
x += getMod();
}
if (x >= getMod()) {
x -= getMod();
}
return x;
}
constexpr int val() const { return x; }
explicit constexpr operator int() const { return x; }
constexpr MInt operator-() const {
MInt res;
res.x = norm(getMod() - x);
return res;
}
constexpr MInt inv() const {
assert(x != 0);
return power(*this, getMod() - 2);
}
constexpr MInt &operator*=(MInt rhs) & {
x = 1LL * x * rhs.x % getMod();
return *this;
}
constexpr MInt &operator+=(MInt rhs) & {
x = norm(x + rhs.x);
return *this;
}
constexpr MInt &operator-=(MInt rhs) & {
x = norm(x - rhs.x);
return *this;
}
constexpr MInt &operator/=(MInt rhs) & { return *this *= rhs.inv(); }
friend constexpr MInt operator*(MInt lhs, MInt rhs) {
MInt res = lhs;
res *= rhs;
return res;
}
friend constexpr MInt operator+(MInt lhs, MInt rhs) {
MInt res = lhs;
res += rhs;
return res;
}
friend constexpr MInt operator-(MInt lhs, MInt rhs) {
MInt res = lhs;
res -= rhs;
return res;
}
friend constexpr MInt operator/(MInt lhs, MInt rhs) {
MInt res = lhs;
res /= rhs;
return res;
}
friend constexpr std::istream &operator>>(std::istream &is, MInt &a) {
i64 v;
is >> v;
a = MInt(v);
return is;
}
friend constexpr std::ostream &operator<<(std::ostream &os, const MInt &a) {
return os << a.val();
}
friend constexpr bool operator==(MInt lhs, MInt rhs) {
return lhs.val() == rhs.val();
}
friend constexpr bool operator!=(MInt lhs, MInt rhs) {
return lhs.val() != rhs.val();
}
};
template <> int MInt<0>::Mod = 998244353;
template <int V, int P> constexpr MInt<P> CInv = MInt<P>(V).inv();
constexpr int P = 998244353;
using Mint = MInt<P>;
int solve(string &a, string &b) {
int n = a.length();
vector<Mint> dp(n + 1), A(n + 1), B(n + 1);
// dp[i] is the expected moves when there are i mismatches b/w the strings.
// Every dp[i] would be a linear function of the form Ax + B.
// Let's maintain 2 arrays A and B to store this linear function.
A[0] = 0, B[0] = 0; // 0*x + 0
A[1] = 1, B[1] = 0; // 1*x + 0
for (int i = 1; i < n; i++) {
// dp[i] = 1 + (1 - p)*dp[i - 1] + p*dp[i + 1]
// p*dp[i + 1] = dp[i] - (1 - p)*dp[i - 1] - 1;
// p is the probability of picking up matched entry.
//
// p = (n - i)/n
// p will never be zero, so we can divide freely.
Mint p = (Mint)(n - i) / n;
Mint denom_inv = 1 / p;
A[i + 1] = denom_inv * (A[i] - (1 - p) * A[i - 1]);
B[i + 1] = denom_inv * (B[i] - (1 - p) * B[i - 1] - 1);
}
// Now, dp[n] would be populated as a linear function.
// However, there's a different way to populate dp[n].
// dp[n] = 1 + dp[n - 1]
// Hence, both these value should be equal.
//
// Ex + F = 1 + Px + Q
// x = (1 + Q - F)/(E - P)
Mint x = (1 + B[n - 1] - B[n]) / (A[n] - A[n - 1]);
for (int i = 0; i <= n; i++) {
dp[i] = A[i] * x + B[i];
}
int mismatch_count = 0;
for (int i = 0; i < n; i++) {
if (a[i] != b[i]) {
mismatch_count++;
}
}
return dp[mismatch_count].val();
}
int main() {
int t;
cin >> t;
for (int zz = 0; zz < t; zz++) {
int n;
cin >> n;
string a, b;
cin >> a >> b;
cout << solve(a, b) << "\n";
}
return 0;
}
