TI 84 calculator oddity (or maybe error)

[jon_leonard]

I was doing something related to Fermat primes, and noticed that my TI-84's interpretation of 2^2^5+1 isn't 4294967297 as I'd expect (famously divisible by 641), but rather 1025: It's interpreting it as ((2^2)^5)+1. How'd they get the order of operations wrong there?

Comments

[prock]

wiki to the rescue: "Calculators may associate exponents to the left or to the right depending on the model. For example..."

[jon_leonard]

Yes... Though to my way of thinking, that's about equivalent to "Some calculators get it wrong."

It seems more likely that they just implemented a fairly simple expression parser, and treated all the same-precedence operators as left-associative. That doesn't matter for addition and multiplication, and it's right for division and subtraction. But it's wrong for exponentiation.