Key identity

The cube series satisfies sum_{k=1}^{n}k^3=left( rac{n(n+1)}{2} ight)^2.

That means the sum of cubes is always the square of the nth triangular number.

Useful checks

  • Verifying algebra practice and induction examples.
  • Comparing a direct sum with the compact formula.
  • Recognizing how quickly higher powers grow.