Problem88.kt

fun productSumFactors(max: Int) = sequence {
    val size = log2(max.toDouble()).toInt() + 1
    val array = List(size) { 1 }.toIntArray()

    while (true) {
        var indexOn = array.size - 1
        array[indexOn]++
        var reduced: Int

        while (array.reduce { acc, i -> acc * i }.also { reduced = it } > max) {
            indexOn--
            if (indexOn < 0) return@sequence
            val nextIndex = array[indexOn]++
            array[indexOn + 1] = nextIndex
        }

        val sum = array.sum()
        val k = size + (reduced - sum)

        yield(FactorResult(k, reduced))
    }
}