28

28 < 27 | 29 >
Numbers 0 - 99
0	1	2	3	4	5	6	7	8	9
10	11	12	13	14	15	16	17	18	19
20	21	22	23	24	25	26	27	28	29
30	31	32	33	34	35	36	37	38	39
40	41	42	43	44	45	46	47	48	49
50	51	52	53	54	55	56	57	58	59
60	61	62	63	64	65	66	67	68	69
70	71	72	73	74	75	76	77	78	79
80	81	82	83	84	85	86	87	88	89
90	91	92	93	94	95	96	97	98	99

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.
• 28 is an even composite number.
• 28 is the 7th triangular number, and therefore the number of tiles in a double-six domino set.
• 28 is equal to the sum of its proper divisors: 1 + 2 + 4 + 7 + 14 = 28. This makes it a perfect number, the neighboring ones being 6 and 496.
• Ignoring Easter, the Julian calendar 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.
• DeepLineMadom calls the number unoo-yodecol.