[1] Bronowski, J.: Mathematical puzzle. New Statesman and Nation, 38 (1949), 981, 761. https://archive.org/details/sim_new-statesman_1949-12-24_38_981

[2] Littlewood, D. E.: 2494. On Note 2298: A digital puzzle. Math. Gazette, 39 (1955), 327, 58. https://www.jstor.org/stable/3611102 DOI 10.2307/3611102

[3] Primrose, E. J. F.: 2495. A digital puzzle. Math. Gazette, 39 (1955), 327, 58–59. https://www.jstor.org/stable/3611103

[4] Pedoe, D.: The Gentle Art of Mathematics. Macmillan, London, 1959. https://archive.org/details/gentleartofmathe0000pedo

[5] Dudeney, H. E.: Amusements in Mathematics. Thomas Nelson and Sons, London, 1917, Problem 126. https://archive.org/details/amusementsinmath00dude

[6] Moree, P.: Artin’s primitive root conjecture – a survey. Integers, 12 (2012), 6, 1305–1416. https://guests.mpim-bonn.mpg.de/moree/surva.pdf DOI 10.1515/integers-2012-0043

[7] Dlab, D.: RotationallyMultiplicativeIntegers. 2026, software, https://github.com/delta42/RotationallyMultiplicativeIntegers