// sum = 1 + 11 + 111 + 1111 + ... N
function sum_of_series(N) {
let sum = 0, tmp = 1, s = "";
for (let i = 0; i < N; i++) {
s += tmp + " ";
if (i < N - 1) {
s += "+ ";
}
sum += tmp;
tmp = (tmp * 10) + 1;
}
console.log(s);
return sum;
}
const N = 6;
const sum = sum_of_series(N);
console.log("= " + sum);
/*
run:
1 + 11 + 111 + 1111 + 11111 + 111111
= 123456
*/