Sieve of Eratosthenes followed by a sum loop:
let sieve_sum n =
let s = Array.make (n + 1) true in
s.(0) <- false;
s.(1) <- false;
for i = 2 to n do
if s.(i) then begin
let j = ref (i * i) in
while !j <= n do
s.(!j) <- false;
j := !j + i
done
end
done;
let total = ref 0 in
for i = 2 to n do
if s.(i) then total := !total + i
done;
!total
Real PE10 asks for sum below 2,000,000; that's a ~2-3 second loop in
native OCaml but minutes-to-hours under our contended-host
spec-level evaluator. 100 keeps the run under 3 minutes while still
exercising the same algorithm.
110 baseline programs total.