Leyland Numbers – Numberphile
Check out this interesting video about Leyland Numbers, numbers of the form 
A curious and open question is: Which Leyland numbers happen to be prime?
Featured book:
Prime Obsession: Bernhard Riemann and the Greatest Unsolved Problem in Mathematics
In 1859, Bernhard Riemann, a little-known thirty-two year old mathematician, made a hypothesis while presenting a paper to the Berlin Academy titled “On the Number of Prime Numbers Less Than a Given Quantity.” Today, after 150 years of careful research and exhaustive study, the Riemann Hyphothesis remains unsolved, with a one-million-dollar prize earmarked for the first person to conquer it.
Alternating passages of extraordinarily lucid mathematical exposition with chapters of elegantly composed biography and history, Prime Obsession is a fascinating and fluent account of an epic mathematical mystery that continues to challenge and excite the world.
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