colnames.c

#include <stdio.h>
#include <string.h>

int main(int argc, char const *argv[])
{
  int i, j, mod;
  char tmp[50] = "";
  char result[50] = "";

  for(i = 1; i < 817; i++) {
    j = i;
    result[0] = '\0';

    while(j > 0) {
      mod = (j - 1) % 26;
      sprintf(tmp, "%c", mod + 65);
      j = (j - mod) / 26;
      strcat(tmp, result);
      sprintf(result, "%s", tmp);
    }

    printf("%s\n", result);
  }

  return 0;
}

gcc colnames.c && ./a.out | column -c 257