#include <stdio.h>
#include <stdlib.h>
#include <time.h>

#define N 1000000

#define TABSIZE 100000
static int primeS[N];

int maketable(void) {
  int n, i, r, q, idx;
  primeS[0] = 2;
  primeS[1] = 3;
  idx = 2;
  for (n = 4; n < N; n++) {
    i = 0;
    do {
      r = n % primeS[i];
      if (r == 0)
        break;
      q = n / primeS[i];
      i++;
    } while (primeS[i] < q);
    if (r > 0) {
      primeS[idx] = n;
      idx++;
      if (idx > TABSIZE) {
        fprintf(stderr, "table size is too small, aborted. idx = %d\n", idx);
        exit(-1);
      }
    }
  }
  return idx;
}

int foundp(int s, int n) {
  int max, min, mid;
  max = n - 1; min = 0;
  while (max > min) {
    mid = (max + min) / 2;
    if (primeS[mid] == s)
      return 1;
    if (primeS[mid] < s)
      min = mid + 1;
    else
      max = mid - 1;
  }
  if (primeS[min] == s)
    return 1;
  return 0;
}

int main() {
  int n, s, p;
  int i, j, k;
  int max_i, max_j, max_k, max_s;
  time_t stt, end;

  stt = time(NULL);
  n = maketable();
  p = primeS[n - 1];
  printf("n = %d(%d)\n", n, p);
  max_i = max_j = max_k = max_s = 0;
  for (i = 0; i < n; i++) {
    s = 0;
    for (k = 1, j = i; j >= 0; --j, k++) {
      s += primeS[j];
      if (s > p)
        break;
      if ((s % 2) && foundp(s, n)) {
        if (k > max_k) {
          max_i = i; max_j = j; max_k = k; max_s = s;
        }
      }
    }
  }
  printf("max prime: %d, series: form %d to %d (%d)\n", max_s, primeS[max_j], primeS[max_i], max_k);
  end = time(NULL);
  printf("time: %d sec\n", end - stt);
  return 0;
}
/* end */

n = 78498(999983)
max prime: 997651, series: form 7 to 3931 (543)
time: 1 sec