Summations or triangular numbers is one of the simplest magic skill to master. It is useful in the study of magic squares and gematria.
If we write SUM( 1..n, n) as T( n), “the triangle of n”, we have the following three properties:
T( n) = n × (n+1) / 2
n² = T( n) + T( n-1)
T( n)² = n³ + T( n-1)² = SUM( 1..n, n³)