How to resolve the algorithm Attractive numbers step by step in the Common Lisp programming language

Published on 12 May 2024 09:40 PM
#Common lisp

How to resolve the algorithm Attractive numbers step by step in the Common Lisp programming language

Table of Contents

Problem Statement

A number is an   attractive number   if the number of its prime factors (whether distinct or not) is also prime.

The number   20,   whose prime decomposition is   2 × 2 × 5,   is an   attractive number   because the number of its prime factors   (3)   is also prime.

Show sequence items up to   120.

Let's start with the solution:

Step by Step solution about How to resolve the algorithm Attractive numbers step by step in the Common Lisp programming language

Source code in the common programming language

(defun attractivep (n)
  (primep (length (factors n))) )

; For primality testing we can use different methods, but since we have to define factors that's what we'll use
(defun primep (n)
  (= (length (factors n)) 1) )

(defun factors (n)
  "Return a list of factors of N."
  (when (> n 1)
    (loop with max-d = (isqrt n)
      for d = 2 then (if (evenp d) (+ d 1) (+ d 2)) do
      (cond ((> d max-d) (return (list n))) ; n is prime
        ((zerop (rem n d)) (return (cons d (factors (truncate n d)))))))))

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