; 1
; 1 1
; 1 2 1
; 1 3 3 1
; 1 4 6 4 1
; . . . .
; I am sure that I have chosen the worst possible way

(define (pasc-step row col num curr-row curr-col)
  (cond
    ((or (< col 0) (> col row)) 0)
    ((or (= col 1) (= col row)) 1)
    ((= curr-row row) num)
    ((or (= col 2) (= col (- row 1))) (- row 1))
    ((or (> col 2) (< col (- row 1))) (pasc-step
          row
          col
          (+ num (if (< curr-col col)
              (pasc-step curr-row (+ curr-col 1) 1 2 2)
              (pasc-step curr-row (- curr-col 1) 1 2 2)))
          (+ curr-row 1)
          (if (< curr-col col) (+ curr-col 1) curr-col)))))

(define (locate-pasc row col)
  (pasc-step row col 1 2 2))

(locate-pasc 2 1)
(locate-pasc 3 2)
(locate-pasc 4 3)
(locate-pasc 5 2)
(locate-pasc 5 4)
(locate-pasc 6 4)
(locate-pasc 7 3)