; happy new year
(define (tri-list n)
(let loop ((i 0) (ts (list 0)))
(if (= n i) (reverse ts)
(loop (+ i 1) (cons (+ i (car ts) 1) ts)))))
(display (tri-list 63)) (newline)
(define (tri n) (* n (+ n 1) 1/2))
(display (tri 63)) (newline)
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