Perfect numbers in Racket

perfect-numbers.rkt

#lang racket

; Prints out perfect numbers < 1000

(define (proper-factors-of n)
	(filter
		(lambda (x) (= 0 (modulo n x)))

		; n is excluded
		(sequence->list (in-range 1 n))))

(define (is-perfect? n)
	(and
		; proper sum requires multiple terms
		(> (length (proper-factors-of n)) 1)

		(= (apply + (proper-factors-of n)) n)))

(display 
	(filter is-perfect? 
		(sequence->list (in-range 1000))))

(newline)