Discussion on: Challenge: find 'Kaprekar numbers'

import java.util.function.IntPredicate;
import java.util.stream.IntStream;

public class FirstSixteenKaprekarNumbers {

  public static void main(String... args) {

    IntPredicate isKaprekar = i -> {
      long square = i * i;
      // first, generate a stream of possible 10-base divisors (if the left side is zero, we're done):
      return IntStream.iterate(10, div -> div * 10).takeWhile(div -> square / div > 0)
          // then, filter out zero right sides:
          .filter(div -> square % div > 0)
          // finally, see if the sum of the parts match the original number:
          .anyMatch(div -> i == square / div + square % div);
    };

    IntStream.concat(IntStream.of(1), IntStream.iterate(2, i -> i + 1).filter(isKaprekar))
      .limit(16)
      .forEach(System.out::println);

    // 1, 9, 45, 55, 99, 297, 703, 999, 2223, 2728, 4879, 4950, 5050, 5292, 7272, 7777
  }
}