Prime factorising 1296, we get,
1296=2×2×2×2×3×3×3×3
=24×34.
We know, a perfect cube has multiples of 3 as powers of prime factors.
Here, number of 2's is 4 and number of 3's is 4.
So we need to divide 2 and 3 from the factorization to make 1296 a perfect cube.
Hence, the smallest number by which 1296 must be divided to obtain a perfect cube is 2×3=6.