Where is Leyland..?

As of June 2008, the largest Leyland number that has been proven to be prime is 2638⁴⁴⁰⁵ + 4405²⁶³⁸ with 15071 digits. From July 2004 to June 2006, it was the largest prime whose primality was proved by elliptic curve primality proving.^[3] There are many larger known probable primes such as 91382⁹ + 9⁹¹³⁸²,^[4] but it is hard to prove primality of large Leyland numbers. Paul Leyland writes on his website: "More recently still, it was realized that numbers of this form are ideal test cases for general purpose primality proving programs. They have a simple algebraic description but no obvious cyclotomic properties which special purpose algorithms can exploit."

Wikipedia, Leyland number, http://en.wikipedia.org/wiki/Leyland_number (optional description here) (as of Jan. 27, 2010, 05:41 GMT).