fun getItem(num: Int): Int = 1 + num * 2

fun getRowRange(num: Int): IntProgression {
    return ((num - 1) * (num) / 2) until (num * (num + 1) / 2)
}

fun getRowValueRange(num: Int): IntProgression =
    getRowRange(num).let { getItem(it.first)..getItem(it.last) step 2 }


fun getRowSum(num: Int): Int =
    getRowValueRange(num).let {
        // a_1 + a_n       a_n - a_1
        // ---------  *  ( --------- + 1 )
        //     2           a_2 - a_1
        ((it.first + it.last) / 2) * ((it.last - it.first) / (it.first + it.step - it.first) + 1)
    }

fun main() {
    println(getRowSum(2))
}