Tanya Khovanova has a paper https://arxiv.org/abs/1110.1556 https://arxiv.org/abs/1110.1556 with a list of some more of these problems with easy solutions that

Tanya Khovanova has a paper https://arxiv.org/abs/1110.1556 https://arxiv.org/abs/1110.1556 with a list of some more of these problems with easy solutions that are hard to find. She calls them "Jewish Problems" because they were used by USSR universities to discriminate against Jewish applicants. The applicants would fail to solve them but the university would justifiably be able to claim they were easy.