# Math Teachers at Play 61

Researching 61 as a number tells us it’s not just prime, but is a twin prime, a cuban prime, the 9th Mersenne prime exponent, and a Pillai prime. That’s primo prime pedigree. It’s a Keith number and thrice Fortunate. (Fortunate numbers are pretty interesting and the subject of an open conjecture.) It’s a centered square number (1+4+8+12+16+20), a centered hexagonal number (1+6+12+18+24) and a centered decagonal number (1+10+20+30); mostly because it’s neighbor 60 is so nice. (Did you see the 60th Math Teachers at Play?) Is there a reason that ∑4n, ∑6n and ∑10n overlap at 60? But the fact that really caught my eye was that 61 is an Euler Zig Zag number. How cool can a number get?

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