A fibonacci pseudo random number generator would not be too hard to keep in mind (two integers modulo a fixed number) and might give you ok results if you choos

A fibonacci pseudo random number generator would not be too hard to keep in mind (two integers modulo a fixed number) and might give you ok results if you choose your parameter well and avoid using the weakest bits as the generated boolean : https://en.wikipedia.org/wiki/Lagged_Fibonacci_generator https://en.wikipedia.org/wiki/Lagged_Fibonacci_generator