use std::io::Read; fn get_word() -> String { let stdin = std::io::stdin(); let mut stdin=stdin.lock(); let mut u8b: [u8; 1] = [0]; loop { let mut buf: Vec<u8> = Vec::with_capacity(16); loop { let res = stdin.read(&mut u8b); if res.unwrap_or(0) == 0 || u8b[0] <= b' ' { break; } else { buf.push(u8b[0]); } } if buf.len() >= 1 { let ret = String::from_utf8(buf).unwrap(); return ret; } } } fn get<T: std::str::FromStr>() -> T { get_word().parse().ok().unwrap() } /// Verified by https://atcoder.jp/contests/abc198/submissions/21774342 mod mod_int { use std::ops::*; pub trait Mod: Copy { fn m() -> i64; } #[derive(Copy, Clone, Hash, PartialEq, Eq, PartialOrd, Ord)] pub struct ModInt<M> { pub x: i64, phantom: ::std::marker::PhantomData<M> } impl<M: Mod> ModInt<M> { // x >= 0 pub fn new(x: i64) -> Self { ModInt::new_internal(x % M::m()) } fn new_internal(x: i64) -> Self { ModInt { x: x, phantom: ::std::marker::PhantomData } } pub fn pow(self, mut e: i64) -> Self { debug_assert!(e >= 0); let mut sum = ModInt::new_internal(1); let mut cur = self; while e > 0 { if e % 2 != 0 { sum *= cur; } cur *= cur; e /= 2; } sum } #[allow(dead_code)] pub fn inv(self) -> Self { self.pow(M::m() - 2) } } impl<M: Mod> Default for ModInt<M> { fn default() -> Self { Self::new_internal(0) } } impl<M: Mod, T: Into<ModInt<M>>> Add<T> for ModInt<M> { type Output = Self; fn add(self, other: T) -> Self { let other = other.into(); let mut sum = self.x + other.x; if sum >= M::m() { sum -= M::m(); } ModInt::new_internal(sum) } } impl<M: Mod, T: Into<ModInt<M>>> Sub<T> for ModInt<M> { type Output = Self; fn sub(self, other: T) -> Self { let other = other.into(); let mut sum = self.x - other.x; if sum < 0 { sum += M::m(); } ModInt::new_internal(sum) } } impl<M: Mod, T: Into<ModInt<M>>> Mul<T> for ModInt<M> { type Output = Self; fn mul(self, other: T) -> Self { ModInt::new(self.x * other.into().x % M::m()) } } impl<M: Mod, T: Into<ModInt<M>>> AddAssign<T> for ModInt<M> { fn add_assign(&mut self, other: T) { *self = *self + other; } } impl<M: Mod, T: Into<ModInt<M>>> SubAssign<T> for ModInt<M> { fn sub_assign(&mut self, other: T) { *self = *self - other; } } impl<M: Mod, T: Into<ModInt<M>>> MulAssign<T> for ModInt<M> { fn mul_assign(&mut self, other: T) { *self = *self * other; } } impl<M: Mod> Neg for ModInt<M> { type Output = Self; fn neg(self) -> Self { ModInt::new(0) - self } } impl<M> ::std::fmt::Display for ModInt<M> { fn fmt(&self, f: &mut ::std::fmt::Formatter) -> ::std::fmt::Result { self.x.fmt(f) } } impl<M: Mod> ::std::fmt::Debug for ModInt<M> { fn fmt(&self, f: &mut ::std::fmt::Formatter) -> ::std::fmt::Result { let (mut a, mut b, _) = red(self.x, M::m()); if b < 0 { a = -a; b = -b; } write!(f, "{}/{}", a, b) } } impl<M: Mod> From<i64> for ModInt<M> { fn from(x: i64) -> Self { Self::new(x) } } // Finds the simplest fraction x/y congruent to r mod p. // The return value (x, y, z) satisfies x = y * r + z * p. fn red(r: i64, p: i64) -> (i64, i64, i64) { if r.abs() <= 10000 { return (r, 1, 0); } let mut nxt_r = p % r; let mut q = p / r; if 2 * nxt_r >= r { nxt_r -= r; q += 1; } if 2 * nxt_r <= -r { nxt_r += r; q -= 1; } let (x, z, y) = red(nxt_r, r); (x, y - q * z, z) } } // mod mod_int macro_rules! define_mod { ($struct_name: ident, $modulo: expr) => { #[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)] pub struct $struct_name {} impl mod_int::Mod for $struct_name { fn m() -> i64 { $modulo } } } } const MOD: i64 = 998_244_353; define_mod!(P, MOD); type MInt = mod_int::ModInt<P>; // https://ferin-tech.hatenablog.com/entry/2019/08/11/%E3%83%A9%E3%82%B0%E3%83%A9%E3%83%B3%E3%82%B8%E3%83%A5%E8%A3%9C%E9%96%93 // Finds f(t) given y[i] = f(x0 + d * i) for 0 <= i < y.len(). // O(y.len() * log MOD)-time fn lagrange_interpolate_one_arithprog(y: &[MInt], x0: MInt, d: MInt, t: MInt) -> MInt { assert_ne!(d, 0.into()); let n = y.len(); let mut sum = MInt::new(0); // (x-x0-d*i)/((x-x0)...(x-x0-d*(n-1)))|_{x=x0+d*i} let mut cur = MInt::new(1); // (t-x0)...(t-x0-d*(n-1)) let mut tprod = MInt::new(1); for i in 1..n { cur *= -d * i as i64; } cur = cur.inv(); for i in 0..n { if t == x0 + d * i as i64 { return y[i]; } tprod *= t - x0 - d * i as i64; } for i in 0..n { sum += y[i] * cur * tprod * (t - x0 - d * i as i64).inv(); if i + 1 < n { cur *= (n - i - 1) as i64; cur *= -MInt::new((i + 1) as i64).inv(); } } sum } // Generated by 2747-helper.rs const STEP: usize = 10000000; const LEN: usize = 100; const FACT_TABLE: [i64; 100] = [ 1, 295201906, 160030060, 957629942, 545208507, 213689172, 760025067, 939830261, 506268060, 39806322, 808258749, 440133909, 686156489, 741797144, 390377694, 12629586, 544711799, 104121967, 495867250, 421290700, 117153405, 57084755, 202713771, 675932866, 79781699, 956276337, 652678397, 35212756, 655645460, 468129309, 761699708, 533047427, 287671032, 206068022, 50865043, 144980423, 111276893, 259415897, 444094191, 593907889, 573994984, 892454686, 566073550, 128761001, 888483202, 251718753, 548033568, 428105027, 742756734, 546182474, 62402409, 102052166, 826426395, 159186619, 926316039, 176055335, 51568171, 414163604, 604947226, 681666415, 511621808, 924112080, 265769800, 955559118, 763148293, 472709375, 19536133, 860830935, 290471030, 851685235, 242726978, 169855231, 612759169, 599797734, 961628039, 953297493, 62806842, 37844313, 909741023, 689361523, 887890124, 380694152, 669317759, 367270918, 806951470, 843736533, 377403437, 945260111, 786127243, 80918046, 875880304, 364983542, 623250998, 598764068, 804930040, 24257676, 214821357, 791011898, 954947696, 183092975, ]; // https://yukicoder.me/problems/no/2747 (3.5) // solved with hints // \sum_{1 <= i <= N} (N-i)i^K が計算できれば良い。これはベルヌーイ数の先頭 K 項が O(K log K)-time 程度で計算できれば計算できる。 // -> 解説を見た。ラグランジュ補間の方が簡単。最終的な多項式は K+2 次なので、0 <= i <= K+2 の K+3 点で補間する。 // 最後に (N-2)! * (N-1) * 2 を掛けること。 // - (N-2)!: 残りの点の埋め方 // - (N-1): どの隙間を見るか // - 2: 左の方が大きいか // Tags: lagrange-polynomial-interpolation, lagrange-interpolation fn main() { let n: i64 = get(); let k: i64 = get(); let mut y = vec![]; let mut sum = MInt::new(0); for i in 0..k + 3 { sum += MInt::new(i).pow(k) * (n - i); y.push(sum); } let mut ans = lagrange_interpolate_one_arithprog(&y, 0.into(), 1.into(), n.into()); ans *= 2; let tbl_idx = ((n - 1) as usize / STEP).min(LEN - 1); let mut fac = MInt::new(FACT_TABLE[tbl_idx]); for i in tbl_idx * STEP + 1..=(n - 1) as usize { fac *= i as i64; } ans *= fac; println!("{ans}"); }