Seven numbers that behave strangely
1729 — Ramanujan's taxicab number: the smallest that's a sum of two cubes in two different ways. Sounds trivial until you try to find another in your head.
0.5772… — the Euler-Mascheroni constant, everywhere in maths, and after centuries nobody knows if it's even rational. And twin primes (11 & 13, 17 & 19) seem endless, yet no one can prove it.
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