--- a/euler.lisp Sat Apr 09 17:16:13 2016 +0000
+++ b/euler.lisp Sun Apr 10 00:58:30 2016 +0000
@@ -1,12 +1,23 @@
(in-package #:euler)
(defun problem-1 ()
+ ;; If we list all the natural numbers below 10 that are multiples of 3 or 5,
+ ;; we get 3, 5, 6 and 9. The sum of these multiples is 23.
+ ;;
+ ;; Find the sum of all the multiples of 3 or 5 below 1000.
(loop :for i :from 1 :below 1000
:when (or (dividesp i 3)
(dividesp i 5))
:sum i))
(defun problem-2 ()
+ ;; Each new term in the Fibonacci sequence is generated by adding the previous
+ ;; two terms. By starting with 1 and 2, the first 10 terms will be:
+ ;;
+ ;; 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, ...
+ ;;
+ ;; By considering the terms in the Fibonacci sequence whose values do not
+ ;; exceed four million, find the sum of the even-valued terms.
(loop :with p = 0
:with n = 1
:while (<= n 4000000)
@@ -15,4 +26,7 @@
n (+ p n))))
(defun problem-3 ()
+ ;; The prime factors of 13195 are 5, 7, 13 and 29.
+ ;;
+ ;; What is the largest prime factor of the number 600851475143 ?
(apply #'max (prime-factorization 600851475143)))