Fairbairn, R. A. “更多關於自守數。”J. Recr. Math.2, 170-174, 1969.Fairbairn, R. A. Erratum to "More on Automorphic Numbers." J. Recr. Math.2, 245, 1969.de Guerre, V. and Fairbairn, R. A. "Automorphic Numbers." J. Recr. Math.1, 173-179, 1968.Hunter, J. A. H. "Two Very Special Numbers." Fib. Quart.2, 230, 1964.Hunter, J. A. H. "Some Polyautomorphic Numbers." J. Recr. Math.5, 27, 1972.Kraitchik, M. "Automorphic Numbers." §3.8 in Mathematical Recreations. New York: W. W. Norton, pp. 77-78, 1942.Madachy, J. S. Madachy's Mathematical Recreations. New York: Dover, pp. 34-54 and 175-176, 1979.Schroeppel, R. Item 59 in Beeler, M.; Gosper, R. W.; and Schroeppel, R. HAKMEM. Cambridge, MA: MIT Artificial Intelligence Laboratory, Memo AIM-239, p. 23, Feb. 1972. http://www.inwap.com/pdp10/hbaker/hakmem/number.html#item59.Sloane, N. J. A. Sequences A003226/M3752, A007185/M3940, A016090, A018247, and A018248 in "The On-Line Encyclopedia of Integer Sequences."Sloane, N. J. A. and Plouffe, S. The Encyclopedia of Integer Sequences. San Diego: Academic Press, 1995.Wells, D. The Penguin Dictionary of Curious and Interesting Numbers. Middlesex, England: Penguin Books, pp. 59 and 171, 178, 191-192, 1986.
使得 
的最後一位（或多位）數字等於 
，被稱為 
-自守數。例如，
(Wells 1986, pp. 58-59) 和 
(Wells 1986, p. 68)，因此 5 和 6 是 1-自守數。類似地，
和 
，因此 8 和 88 是 2-自守數。de Guerre 和 Fairbairn (1968) 給出了自守數的歷史。
的自守數 (Madachy 1979)。前幾個以 5 結尾的 1-自守數是 5, 25, 625, 0625, 90625, ... (OEIS A007185)，前幾個以 6 結尾的 1-自守數是 6, 76, 376, 9376, 09376, ... (OEIS A016090)。以 5 結尾的 1-自守數 
是 冪等元 (mod 
)，因為![[a(n)]^2=a(n) (mod 10^n)](/images/equations/AutomorphicNumber/NumberedEquation1.svg)
-自守數。
-自守數