Put a positive digit in each empty white square so that each odd number is equal to the number of adjacent even numbers, and each even number is equal to the number of adjacent odd numbers. Adjacent means horizontally, vertically, or diagonally.

1. | 2. | 3. | 4. | 5. | 6. |

7. | 8. | 9. | 10. | 11. |

12. | 13. | 14. | 15. |

16. | 17. | 18. | 19. |

20. | 21. | 22. | 23. |

The solutions are here.