def sum_factorials(n, cache=[0, 1]):
    if len(cache) > n:
        return cache[n]
    previous = sum_factorials(n - 1)
    cache.append((previous - sum_factorials(n - 2)) * n + previous)
    return cache[n]
 
def f(n, i=1, factorial=1, result=1):
  if i == n:
    return result
  next = factorial * (i + 1)
  return f(n, i + 1, next, result + next)
 
import time
start = time.time()
result = sum_factorials(980)
print(time.time() - start)
 
start = time.time()
result2 = f(980)
print(time.time() - start)

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