[goldbux]

"It's the 27 Club (prime number) . . ."
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27 is odd, but not prime. 3^3 = 27.

The element with atomic number 27 is Cobalt [Co].

[goldbux]

Moar cubes for yer sliding cubicle . . .
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27 is the smallest cube of three known cubes that have only prime digits.

The other cubes are 3,375 [cube root = 15], and

2,775,577,757,352,755,375,573,357,273 [cube root = 1,405,349,897].

Thanks to all who inquired.