repdigit

English edit

WOTD – 20 August 2018

The number 7777 on this Washington, D.C., vehicle license plate is a repdigit

Etymology edit

Pronunciation edit

(Received Pronunciation, General American) IPA^(key): /ˈɹɛpˌdɪd͡ʒɪt/
- Audio (Southern England) (file)
Hyphenation: rep‧di‧git

Noun edit

Examples
7 11 666 9,999

repdigit (plural repdigits)

(recreational mathematics) A number composed only of one or more occurrences of one specific digit and no other digit.
- 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:
  Repdigit Triangular Numbers [article title]
- 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:
  Is there any system of notation in which there is a repdigit $aa$ such that $(aa)^{2}=ccdd$ , with $c=a-1$ and $d=c-1$ ?
- 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:
  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.
- 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:
  A positive with repeated digit is called a repdigit, for example 222, 55555, and all repunits are repdigits.