Solving using bessel 's formula
for ( int i = 1 ; i < n ; i ++ ) { if ( ( i % 2 ) > 0 ) sum = sum + ( ( u - 0.5 ) * ucal ( u , i - 1 ) * y [ k , i ] ) / fact ( i ) ; else sum = sum + ( ucal ( u , i ) * ( y [ k , i ] + y [ -- k , i ] ) / ( fact ( i ) * 2 ) ) ; } System . Console . WriteLine ( " Value ▁ at ▁ " + value + " ▁ is ▁ " + System . Math . Round ( sum , 5 ) ) ; } }