HP-42S (Free42, DM-42) mini-challenge – Wallis Product

[Werner]

I came up with the same formula, Valentin.
It can be simplified a lot:

Code:

00 { 27-Byte Prgm }
01▸LBL "WP"
02 ENTER
03 STO+ ST Y
04 COMB
05 4
06 LASTX
07 Y↑X
08 LASTX
09 X<> ST Z
10 ÷
11 X↑2
12 X<>Y
13 0.5
14 +
15 ÷
16 END

Blame it on the 4 am ;-)
Cheers, Werner