A nice mathematical thing worked out.

Nice_math.cpp

#include <iostream>
#include <string>
using namespace std;

typedef unsigned long long ui;

int main() {
    char t[20];
    for(ui i=1;i<=9;++i){
        for(char j=0;j<i;++j) {t[j]=(char)49+j; t[i+1]=0;}
        ui cijfer1{stoi(t)};
        cout << cijfer1 << " x 8 + " << i << " = ";
        cout << cijfer1 * 8 + i;
        cout << endl;
    }
    return 0;
}

When this picture was posted by a Twitter friend of mine I simply had to try this out. And see here the result.

(Below a 'playground' screenshot).