Computes 2^n via for-loop multiplication, then walks the digits via
mod 10 / div 10:
let euler16 n =
let p = ref 1 in
for _ = 1 to n do p := !p * 2 done;
let sum = ref 0 in
let m = ref !p in
while !m > 0 do
sum := !sum + !m mod 10;
m := !m / 10
done;
!sum
euler16 15 = 3 + 2 + 7 + 6 + 8 = 26 (= digit sum of 32768)
Real PE16 asks for 2^1000 which exceeds float precision; 2^15 stays
safe and exercises the same digit-decomposition pattern.
115 baseline programs total.
giles
391a2d0c4f