toBigInteger

inline fun Int.toBigInteger(): BigInteger(source)

import java.math.BigInteger

fun main() {
    val smallNumber: Int = 123456
    val bigInt: BigInteger = smallNumber.toBigInteger()
    val doubled = bigInt * 2.toBigInteger()

    println("Small: $smallNumber")
    println("Big: $bigInt")
    println("Doubled: $doubled")
}