Sum of the first N terms of the series 5 , 12 , 23 , 38. ... | Function to calculate the sum ; number of terms to be included in sum ; find the Sn
function calculateSum ( n ) { return 2 * ( n * ( n + 1 ) * ( 2 * n + 1 ) / 6 ) + n * ( n + 1 ) / 2 + 2 * ( n ) ; } let n = 3 ; document . write ( " " + calculateSum ( n ) ) ;