Language: C++

#pragma region Macros
#pragma GCC optimize("O3")
#include <bits/stdc++.h>
#define rep(i, n) for(int i = 0; i < n; ++i)
using namespace std;
#pragma endregion
// from https://judge.yosupo.jp/submission/5147
int primes[100000]={2,3,5};
void prime_sieve(const int N, const int Q = 17, const int L = 1 << 15) {
    using u8 = unsigned char;
    static const int rs[] = {1, 7, 11, 13, 17, 19, 23, 29};
    struct P {
        P(int p) : p(p) {}
        int p;
        int pos[8];
    };
    auto approx_prime_count = [](const int N) -> int { return N > 60184 ? N / (log(N) - 1.1) : max(1., N / (log(N) - 1.11)) + 1; };

    const int v = sqrt(N), vv = sqrt(v);
    vector<bool> isp(v + 1, true);
    for(int i = 2; i <= vv; ++i)
        if(isp[i]) {
            for(int j = i * i; j <= v; j += i) isp[j] = false;
        }

    const int rsize = approx_prime_count(N + 30);
    int psize = 3;

    vector<P> sprimes;
    size_t pbeg = 0;
    int prod = 1;
    for(int p = 7; p <= v; ++p) {
        if(!isp[p]) continue;
        if(p <= Q) prod *= p, ++pbeg, primes[psize++] = p;
        auto pp = P(p);
        for(int t = 0; t < 8; ++t) {
            int j = (p <= Q) ? p : p * p;
            while(j % 30 != rs[t]) j += p << 1;
            pp.pos[t] = j / 30;
        }
        sprimes.push_back(pp);
    }

    vector<u8> pre(prod, 0xFF);
    for(size_t pi = 0; pi < pbeg; ++pi) {
        auto pp = sprimes[pi];
        const int p = pp.p;
        for(int t = 0; t < 8; ++t) {
            const u8 m = ~(1 << t);
            for(int i = pp.pos[t]; i < prod; i += p) pre[i] &= m;
        }
    }

    const int block_size = (L + prod - 1) / prod * prod;
    vector<u8> block(block_size);
    u8 *pblock = block.data();
    const int M = (N + 29) / 30;

    for(int beg = 0; beg < M; beg += block_size, pblock -= block_size) {
        int end = min(M, beg + block_size);
        for(int i = beg; i < end; i += prod) { copy(pre.begin(), pre.end(), pblock + i); }
        if(beg == 0) pblock[0] &= 0xFE;
        for(size_t pi = pbeg; pi < sprimes.size(); ++pi) {
            auto &pp = sprimes[pi];
            const int p = pp.p;
            for(int t = 0; t < 8; ++t) {
                int i = pp.pos[t];
                const u8 m = ~(1 << t);
                for(; i < end; i += p) pblock[i] &= m;
                pp.pos[t] = i;
            }
        }
        for(int i = beg; i < end; ++i) {
            for(int m = pblock[i]; m > 0; m &= m - 1) { primes[psize++] = i * 30 + rs[__builtin_ctz(m)]; }
        }
    }
    assert(psize <= rsize);
    while(psize > 0 && primes[psize - 1] > N) --psize;
    return ;
}
char reader[10000000];
template <const int sz = 5 * 10000000, typename T = long long> struct IO {
    char *now, *now2 = writer;
    IO() {
        reader[fread(reader, sizeof(char), sizeof(char) * sz, stdin)];
        now = reader;
    }
    inline T read() {
        while(*now && *now <= 32) now++;
        if(*now == '-') {
            now++;
            T res = 0;
            while('0' <= *now and *now <= '9') { res = res * 10 + *now++ - '0'; }
            return -res;
        } else {
            T res = 0;
            while('0' <= *now and *now <= '9') { res = res * 10 + *now++ - '0'; }
            return res;
        }
    }
};
// read(), write(T x)
IO<10000000, int> io;
constexpr int N = 1000001;
short c[N];
int a[200001];
int ans, n;
main() {
    n = io.read();
    rep(i, n) a[i] = io.read();
    rep(i, n) c[a[i]]++;
    prime_sieve(N);
    rep(i,78498) {
        for(int j = 1, jj = primes[i]; jj < N; j++, jj += primes[i]) c[jj] += c[j];
    }
    rep(i, n) if(c[a[i]] == 1)++ ans;
    printf("%d",ans);
    return 0;
}


Compiler output:
a.cc:83:24: error: 'writer' was not declared in this scope; did you mean 'write'?
   83 |     char *now, *now2 = writer;
      |                        ^~~~~~
      |                        write
a.cc:108:1: warning: ISO C++ forbids declaration of 'main' with no type [-Wreturn-type]
  108 | main() {
      | ^~~~