Function to find n 'th Bell Number
function bellNumber ( n ) { let bell = new Array ( n + 1 ) ; for ( let i = 0 ; i < n + 1 ; i ++ ) { bell [ i ] = new Array ( n + 1 ) ; } bell [ 0 ] [ 0 ] = 1 ; for ( let i = 1 ; i <= n ; i ++ ) {