The BESSELY () is an engineering function which takes x, n as argument and returns the Bessel function, Yn(x) for a specified order and value of x.
Syntax: BESSELY(X, N)
The BESSELY function syntax has the following arguments:
 X Required. The value at which to evaluate the function.

N Required. The order of the function. If n is not an integer, it is truncated.
Example: Let’s look at some Excel BESSELY function examples and explore how to use the BESSELY function as a worksheet function in Microsoft Excel:
Syntax: =BESSELY(A2,B2)
Result:
Based on the Excel spreadsheet above, the following BESSELY examples would return:
Syntax: =BESSELY(A3,B3)
Result: 0.412308627
Syntax: =BESSELY(A4,B4)
Result: 0.781212821
Syntax: =BESSELY(A5,B5)
Result: 0.107032432
Syntax: =BESSELY(A6,B6)
Result: 0.412308627
Syntax: =BESSELY(A7,B7)
Result: 0.146267163
Syntax: =BESSELY(A8,B8)
Result: 12.78985516
Syntax: =BESSELY(A9,B9)
Result: #NUM!
Syntax: =BESSELY(A10,B10)
Result: #NUM!
Note:
 If x is nonnumeric, BESSELY returns the #VALUE! error value.
 If n is nonnumeric, BESSELY returns the #VALUE! error value.
 If n < 0, BESSELY returns the #NUM! error value.

The nth order Bessel function of the variable x is: