The Prime Glossary: period of a prime

period of a prime
(another Prime Pages' Glossary entries)

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Let p be a prime. The period of the decimal expansion of 1/p is often called the period of p. This period always divides p-1 and usually found by calculating the order of 10 modulo p (which equals the period). If the period equals p-1, then it is a full period prime.

**Period of 1/p (for primes p)**
p	period	p	period	p	period	p	period	p	period	p	period
2	*	3	1	5	*	7	6	11	2	13	6
17	16	19	18	23	22	29	28	31	15	37	3
41	5	43	21	47	46	53	13	59	58	61	60
67	33	71	35	73	8	79	13	83	41	89	44
97	96	101	4	103	34	107	53	109	108	113	112
127	42	131	130	137	8	139	46	149	148	151	75
157	78	163	81	167	166	173	43	179	178	181	180
191	95	193	192	197	98	199	99	211	30	223	222
227	113	229	228	233	232	239	7	241	30	251	50
257	256	263	262	269	268	271	5	277	69	281	28

See Also: UniquePrime