| Number | Name | Date | Kind |
|---|---|---|---|
| 1709660 | De Bracht | Apr 1929 | |
| 2942356 | Weintraub | Jun 1960 | |
| 3091870 | Sangster | Jun 1963 | |
| 3837652 | Kuwagaki et al. | Sep 1974 |
| Number | Date | Country |
|---|---|---|
| 52,215 | Sep 1936 | DK |
| Entry |
|---|
| Martin Gardner's New Mathematical Diversions from Scientific American, publ. by Simon & Schuster, New York, 1966, pp. 82-90. |