Sum of the first N terms of the series 2 , 6 , 12 , 20 , 30. ... | Function to calculate the sum ; number of terms to be included in the sum ; find the Sn
function calculateSum ( n ) { return n * ( n + 1 ) / 2 + n * ( n + 1 ) * ( 2 * n + 1 ) / 6 ; } let n = 3 ; document . write ( " " + calculateSum ( n ) ) ;