(defun e-28 ()
  (+ 1 (loop :for n :from 3 :to 1001 :by 2
             :sum (+ (* 4 (expt (- n 2) 2))
                     (* 10 (- n 1))))))

CL-USER> (e-28)
669171001

— Me@2025-06-13 11:01:45 PM

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