Perimeter of Ellipse

[Werner]

Look closely, Bob, that's not an 'n' ;-)
And I'm afraid to say that any mathematical formula that requires degrees mode for the arcsin is suspicious, to say the least.
Let's try it with A=10 and B=50 (it requires B>=A), Albert's example from above.
Then the result is 214.6..
So not even a very good approximation..

Cheers, Werner