A Lucas number, L15 specifically. Lucas numbers are generated like fibonacci numbers but with a starting set of 1,3 instead of 1,1. L15 is the largest Lucas number that is (a) prime and (b) has a composite index. How anybody can prove that, I don't know, but it's a pretty astonishing fact.



2221 = 1^2 + 1^3 + 2^5 + 3^7
That is, the sum of the first four fibonacci numbers raised to the power of the first four primes.



One of several primes built out of the first four integers. Oddly enough, you can't construct ANY primes from the first 2 integers, nor the first 3, nor the first 5 nor the first 6. Savor the moment.

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