Prime Number Checker

Enter a whole number (up to 500 digits):

Enter a number above to check if it is prime or composite.

What is a Prime Number?

A prime number is a whole number greater than 1 that is only divisible by 1 and itself. In other words, a prime number has only two factors, 1 and itself. A number that is not a prime is a composite number which means it has more than two factors.

How the Prime Checker Works

For numbers under 15 digits, this calculator uses Prime Factorization. It divides the number by prime numbers up to its square root. If the number is composite and less than 15 digits long, the calculator lists all factors found.

For large numbers (more than 15 digits and up to 500 digits), this calculator uses the robust Miller–Rabin primality test. Since the calculation can become highly resource-intensive, the test returns either “Composite” or “Probable Prime” for numbers over 25 digits long.

Is 1 a Prime Number?

No. Since the only factor of 1 is 1, it does not meet the criteria of having exactly two distinct factors (1 and itself). 1 is considered neither prime nor composite.

Prime Numbers 1-109 Table

There are 25 prime numbers between 1 and 100. This table lists the first 109 prime numbers. Hover your cursor over a cell to see its rank (e.g., Prime[13] = 41).

Range	+0	+1	+2	+3	+4	+5	+6	+7	+8	+9
1-9		2	3	5	7
10-19	11	13	17	19
20-29	23	29	31	37	41	43	47	53	59	61
30-39	67	71	73	79	83	89	97	101	103	107
40-49	109	113	127	131	137	139	149	151	157	163
50-59	167	173	179	181	191	193	197	199	211	223
60-69	227	229	233	239	241	251	257	263	269	271
70-79	277	281	283	293	307	311	313	317	331	337
80-89	347	349	353	359	367	373	379	383	389	397
90-99	401	409	419	421	431	433	439	443	449	457
100-109	461	463	467	479	487	491	499	503	509	521

Prime Numbers 1-1000

There are 168 prime numbers between 1 and 1000. For a complete, searchable list, you can refer to external resources.