Srinivasa Ramanujan

Srinivasa Ramanujan: one of the best mathematicians of all time. He had no formal training in maths and yet he managed to unintentionally discover taxicab numbers. This is related to the story of G.H. Hardy (who discovered Ramanujan's talent) visited Ramanujan and having travelled in a taxicab numbered 1729. He commented that this number seemed to be uninteresting but Ramanujan replied immediately that it is very interesting because it is the smallest natural number that can be expressed as the sum of two cubes in two different ways. So far, six taxicab numbers have been discovered.
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Stupidly Difficult Challenge

Find the seventh Taxicab number.

The first problem that Ramanujan posed was what is the answer to this problem:
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This is the answer he found:
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So basically, 3.