Is there a similar function to the HP-27S Summing {** sigma**} Function (page 108 of Owner's Manual) but available on the HP-42S or the HP-32SII and in the related owner's manual(s)? I can't seem to find one but I could have overlooked it.

FYI, from HP-27S manual:

{** sigma**}(counter variable : starting value : ending value : step size : algebraic expression)

Definition: Sums values of the algebraic expression for values of the counter variable. The counter variable starts with the starting value and is incremented in steps to a final ending value.

I'd like to try out the following equation in SOLVE on my 42S and 32SII if possible.

Solve for PI' (since PI is already a function):

PI'=(6÷SQRT(3))*{** sigma**}(I:0:LAST:1:(-1)^I÷((2xI+1)x3^I))

It takes a value of 21 in variable LAST to produce 12 digits of accuracy (last digit rounded up) for PI'.

Ref: The history of the approximation of the number PI; 4.1. Gottfried Wilhelm Leibniz (1646-1716); Scholz, Werner; http://cwscholz.net/projects/fba/fba.html

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Confounded ... how, if even possible, do I embed special characters like the {** sigma**} symbol (Σ) into a forum message? :-/