(a) brute force == recurrence for n<=10: OK
(a') row sums == E_n (sec+tan), n<=400: OK
(b) even-row tangent formula and odd-row secant formula, rows<=400, mismatches: 0
(c) refined bound violations for n<=2000: 0  (entries where bound is attained: 1281144 )
(d) Stern for all pairs 0<=n<m<=200 (exact), failures: 0
(e) my numpy E_n mod 2^64 == finder C output for n<=70000: True
real 15.81
user 15.00
sys 0.66
