Assessment of practical C-language skills Task1

#include <stdio.h>
#include <math.h>

int main(void) {
    int n;
    scanf("%d", &n);
    int sum = 0;
    float mean = 0.0, SD = 0.0;
    sum = ((1+n)*n)/2;
    mean = sum / n;
    for (int i = 1; i <= n; ++i) {
        SD += pow((double)i - mean, 2);
        printf("%d", i);
        if (i == n)
            printf("\n");
        else
            printf(",");
    }
    SD = sqrt(SD/(n-1));
    int last_even_number = (n/2)*2;
    int even_numbers = (last_even_number - 2) / 2 + 1;
    int last_divided_by_13 = (n/13)*13;
    int sum_dividable_by_13 = (13 + last_divided_by_13) * ((last_divided_by_13 - 13)/13+1) / 2;
    printf("a) %.1f\nb) %.2f\nc) %d\nd) %d\ne) %d\n", mean, SD, sum, even_numbers, sum_dividable_by_13);
    return 0;
}