1111111111111111111
This number is a prime.
111111111 1111111111
1 1 1
1 1 1 1
1 1 1 1 1
1 1 1 1
1 1 1
A repunit hex-congruent prime in bases 11 and 12. [Dobb]
The largest prime factor of the alternate-digit, palindromic semiprime 1010101010101010101010101010101010101 is the repunit prime 1111111111111111111. Both numbers contain 19 1's. [Green]
The second repunit prime. [Gronos]
1111111111111111111^2 = 1111111111111111111 (mod 11111111111111111111111111111111111111). [Luhn]
The second (and largest known) repunit prime to be prime in both decimal and binary. [Green]
|
Each of the 10 palindromes in the trapezoidal structure to the right contains 19 ones, and the repunit prime, R19, is the largest prime factor of each one. |
1111111111111111111 101111111111111111101 10101111111111111110101 1010101111111111111010101 101010101111111111101010101 10101010101111111110101010101 101010101010111111101010101010 101010101010101111101010101010101 10101010101010101110101010101010101 1010101010101010101010101010101010101 |
The seventh Mersenne prime (219-1) written in binary.
The smallest prime Kaprekar number. E.g., 1111111111111111111^2 =
1234567901234567900987654320987654321 and 123456790123456790 + 0987654320987654321 =
1111111111111111111. [Rivera]
11*11*1111111111111111111 = R(2)*R(2)*R(19) = 134444444444444444431, four palindromes. The first three, 11, 11 and 1111111111111111111, are palindromic primes. Note that the concatenation of these three palprimes is R(2).R(2).R(19) = R(23) = 11111111111111111111111. Found by Giovanni Resta. [Rivera]