RPNator

Features:
- Minimalistic design with large buttons.
- Long press for alternate function.
- Postfix notation (to calculate 2*3+4*5, press 2, ENTER, 3, *, 4, ENTER, 5, *, +).
- Unlimited stack.
- Three-line display.
- 16 digits precision.

Operations:
CE / AC - clear entry / clear all stack
LOAD / save - copy saved number to the top / save the current number
ENTER / drop - add the current number to the top / remove the top number
sin / asin - sine / arcsine
cos / acos - cosine / arccosine
tan / atan - tangent / arctangent
exp / pow - exponential / nth power function
sqrt/ cbrt - square / cube root
x^2 / x^3 - square / cube
1/x / root - 1/x / nth root
ln / log - natural logarithm / logarithm to base n
n! - factorial of n (n -- n!)
ncr - number of different, unordered combinations of r objects from a set of n objects (n r -- nCr)
npr - number of possibilities for choosing an ordered set of r objects (a permutation) from a total of n objects (n r -- nPr)
rand - random number in a range (a b -- random from a to b)
rad - convert from degrees to radians ( x -- x * pi / 180)
deg - convert from radians to degrees ( x -- x * 180 / pi)
pi - enter the PI number ( -- pi)