Solution to: Prime numbers with equal digits

by Christoph Lohe

In the decimal number system, the first prime number candidates with equal digits are:

[2] = 11 is a prime number
[3] = 111 = 3 x 37
[5] = 11111 = 41 x 271
[7] = 1111111 = 239 x 4649
[11] = 11111111111 = 21649 x 513239
[13] = 1111111111111 = 53 x 79 x 265371653
[17] = 11111111111111111 = 2071723 x 5363222357
[19] = 1111111111111111111 is a prime number

An open question remains whether there is a largest prime number with equal "1" digits - I don't know the answer. If you find a prime number beyond [19], or if you know about a free prime test program or an online prime test link for numbers with more than 20 digits then please let me know.

		updated: 09.01.2004