28

28 (twenty-eight) is a positive integer following 27 and preceding 29. Its ordinal form is written "28th" or "twenty-eighth".
== Properties ==
*28 is the second perfect number.MathWorld, Perfect Number
*28 is an .
*28 is the 7th , and therefore the number of tiles in a double-six set.
*28 is equal to the sum of its proper divisors: 1 + 2 + 4 + 7 + 14 = 28. This makes it a , the neighboring ones being 6 and 496.
*Ignoring Easter, the repeats every 28 years.
== In googology ==
In Greek-based number-naming systems, 28 is associated with prefix "octoicosa-", and with prefix "octoviginti-" in Latin systems.
== Sources ==
Category:Numbers
Category:Calendar-related numbers
Category:Class 1
Category:Domino-related numbers
Category:Numbers 0-99
Category:Numbers with 1 to 2 digits
Category:Perfect numbers