Merge pull request #5517 from oWnOIzRi/week147

add solution week 147 task 2 in perl and javascript

1 files changed, 38 insertions, 0 deletions

diff --git a/challenge-147/steven-wilson/javascript/ch-02.js b/challenge-147/steven-wilson/javascript/ch-02.js
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+++ b/challenge-147/steven-wilson/javascript/ch-02.js
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+#!/usr/bin/env node
+// Week 147 Task 2
+// Pentagon Numbers
+// Write a sript to find the first pair of Pentagon Numbers
+// whose sum and difference are also a Pentagon Number.
+// Answer: First pair is 1560090 and 7042750
+
+var pentagonal_numbers = [1]
+var pair_found = false
+var number = 2
+
+while (!pair_found) {
+	let next_pn = pentagonal_number(number)
+	for (let i = 0; i < pentagonal_numbers.length; i++) {
+		if ((is_pentagonal_number(next_pn - pentagonal_numbers[i])) && 
+			(is_pentagonal_number(next_pn + pentagonal_numbers[i]))) {
+			console.log('First pair are ' + pentagonal_numbers[i] + ' and ' + next_pn)
+			pair_found = true
+			break
+		}
+	}
+	pentagonal_numbers.push(next_pn)
+	number++
+}
+
+function pentagonal_number (number) {
+	return ( ( 3 * ( number * number ) ) - number ) / 2
+}
+
+function is_pentagonal_number (number) {
+	let remainder = ( Math.sqrt( 24 * number + 1 ) + 1 ) % 6;
+    if ( remainder > 0 ) {
+    	return false
+    }
+    else {
+    	return true
+    }
+}