# Documentation/Calc Functions/BESSELK

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## Function name:

BESSELK

## Category:

Add-in

## Summary:

Calculates the modified Bessel function of the second kind Kn(x).

## Syntax:

BESSELK(**X**; **N**)

## Returns:

## Arguments:

**X** is the strictly positive value (X > 0) on which the function will be calculated.

**N** is a positive integer (N >= 0) representing the order of the Bessel function Kn(x)

## Additional details:

## Examples:

=BESSELK(3.45, 4), returns 0.144803466373734

=BESSELK(3.45, 4.333), returns 0.144803466373734, same as above because the fractional part of N is ignored.

=BESSELK(0, 3), returns Err:502 – invalid argument (X=0)