repdigit

plural repdigits

1. recreational mathematicsA number composed only of one or more occurrences of one specific digit and no other digit.

   Repdigit Triangular Numbers [article title]

   1975, David W. Ballew, Ronald C. Weger, “Repdigit Triangular Numbers”, in Journal of Recreational Mathematics, volume 8, number 2, Farmingdale, N.Y.: Baywood Publishing Co., →ISSN, →OCLC, pages 96–98

   3 more examples

   Is there any system of notation in which there is a repdigit aa such that (aa)²#61;ccdd, with c#61;a-1 and d#61;c-1?

   1980 January, Murray S[eymour] Klamkin, quoting Charles W. Trigg, “The Olympiad Corner: 11”, in Crux Mathematicorum, volume 6, number 1, Ottawa, Ont.: Canadian Mathematical Society, →ISSN, →OCLC, page 16

   Here is another palindromic magic square that has the added property of having main diagonals containing eight repeating "repdigits": 222, 333, 444, 555, 666, 777, 888, and 999. The magic sum is 2442.

   2002, Clifford A[lan] Pickover, “Gallery I: Squares, Cubes, and Tesseracts”, in The Zen of Magic Squares, Circles, and Stars: An Exhibition of Surprising Structures across Dimensions, Princeton, N.J.; Woodstock, Oxfordshire: Princeton University Press, →ISBN, page 284

   A positive with repeated digit is called a repdigit, for example 222, 55555, and all repunits are repdigits.

   2005, James J[oseph] Tattersall, “Modular Arithmetic”, in Elementary Number Theory in Nine Chapters, 2nd edition, Cambridge: Cambridge University Press, →ISBN, section 5.6 (Supplementary Exercises), paragraph 14, page 193