ThreePower ← (=0/+◿3⊕⧻.⊛°/×|1)=0.

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⍤"0 is a power of 3" ThreePower 0
⍤"1 is a power of 3" ThreePower 1
⍤"8 is a power of 3" ThreePower 8
⍤"27 is a power of 3" ThreePower 27
⍤"64 is a power of 3" ThreePower 64
⍤"1000 is a power of 3" ThreePower 64

⍤"9 is not a power of 3" ¬ ThreePower 9
⍤"54 is not a power of 3" ¬ ThreePower 54
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