[ February 17, 2002 ]
An interesting tetradic prime
Dubner and Broadhurst

[ Extra info ( The PrimePages ) ] Tetradic Prime

As a result of a recent major search for base 10 factors,
( 10¹⁵⁶⁰⁰ – 1 ) is now approximately 30.09 % factored.
This allowed a search for interesting large primes
that could be certified prime.

After a lucky short search by Dubner and Broadhurst
we found the prime (with 15601 digits - btw # is also prime)

P = 1808010808 * R(15600) * 10 / R(10) + 1. or P = 1808010808 repeated 1560 times, then ending with an additional 1.

Broadhurst certified primality.
He also found many of the key base 10 factors.

This is a tetradic (4-way) prime: It is a palindrome as well
as the same upside down and mirror reflected.
The only larger tetradic primes have long strings of zeros.
The above P is much more interesting.

However there is a problem. This prime is too small for
Chris Caldwell's current Titanic prime list. It is even too small
for his top 20 palindromic prime list. At least all you people
will know about it even if it may not be saved for posterity.

Harvey Dubner

OEIS sequences A006072 and A068188.
Prime Curios! 186690061, 188888881 and 10080...08001
Palindromic Primes webpage Palprim2.htm