From a45e411521f3f0b2522cc95e96cdae1942d6b90f Mon Sep 17 00:00:00 2001
From: fun-guava <fun-guava@users.noreply.github.com>
Date: Sun, 27 Nov 2022 16:53:19 +0100
Subject: [PATCH 1/3] Added FriendlyNumbers.js, to determine if two integers
 are friendly numbers

---
 Maths/FriendlyNumbers.js | 41 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 41 insertions(+)
 create mode 100644 Maths/FriendlyNumbers.js

diff --git a/Maths/FriendlyNumbers.js b/Maths/FriendlyNumbers.js
new file mode 100644
index 0000000000..2c7115ee72
--- /dev/null
+++ b/Maths/FriendlyNumbers.js
@@ -0,0 +1,41 @@
+/*
+  'In number theory, friendly numbers are two or more natural numbers with a common abundancy index, the
+  ratio between the sum of divisors of a number and the number itself.'
+  Source: https://en.wikipedia.org/wiki/Friendly_number
+  See also: https://mathworld.wolfram.com/FriendlyNumber.html#:~:text=The%20numbers%20known%20to%20be,numbers%20have%20a%20positive%20density.
+*/
+
+export const FriendlyNumbers = (firstNumber, secondNumber) => {
+  // input: two integers
+  // output: true if the two integers are friendly numbers, false if they are not friendly numbers
+
+  // First, check that the parameters are valid
+  if (!Number.isInteger(firstNumber) || !Number.isInteger(secondNumber) || firstNumber === 0 || secondNumber === 0 || firstNumber === secondNumber) {
+    throw new Error('The two parameters must be distrinct, non-null integers')
+  }
+
+  // Calculate the abundancy index of the two number.
+  // ... first get the sum of their divisors
+  let sumDivisorsFirstNumber = firstNumber
+  let sumDivisorsSecondNumber = secondNumber
+
+  for (let i = 0; i < firstNumber / 2; i++) {
+    if (Number.isInteger(firstNumber / i)) {
+      sumDivisorsFirstNumber += i
+    }
+  }
+  for (let i = 0; i < secondNumber / 2; i++) {
+    if (Number.isInteger(secondNumber / i)) {
+      sumDivisorsSecondNumber += i
+    }
+  }
+  // ... and divide that sum by the number itself
+  const abundancyIndexFirstNumber = sumDivisorsFirstNumber / firstNumber
+  const abundancyIndexSecondNumber = sumDivisorsSecondNumber / secondNumber
+
+  if (abundancyIndexFirstNumber === abundancyIndexSecondNumber) {
+    return true
+  } else {
+    return false
+  }
+}

From 27cf17619bf3ecc118e1c02e1c1711be64e1311c Mon Sep 17 00:00:00 2001
From: fun-guava <fun-guava@users.noreply.github.com>
Date: Sun, 27 Nov 2022 17:14:06 +0100
Subject: [PATCH 2/3] Fixed a typo in the error message

---
 Maths/FriendlyNumbers.js | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Maths/FriendlyNumbers.js b/Maths/FriendlyNumbers.js
index 2c7115ee72..7ba69e90b3 100644
--- a/Maths/FriendlyNumbers.js
+++ b/Maths/FriendlyNumbers.js
@@ -11,7 +11,7 @@ export const FriendlyNumbers = (firstNumber, secondNumber) => {
 
   // First, check that the parameters are valid
   if (!Number.isInteger(firstNumber) || !Number.isInteger(secondNumber) || firstNumber === 0 || secondNumber === 0 || firstNumber === secondNumber) {
-    throw new Error('The two parameters must be distrinct, non-null integers')
+    throw new Error('The two parameters must be distinct, non-null integers')
   }
 
   // Calculate the abundancy index of the two number.

From 7ce4bf3e1cb351d33821ebd039142a9271fea6b4 Mon Sep 17 00:00:00 2001
From: fun-guava <fun-guava@users.noreply.github.com>
Date: Sun, 27 Nov 2022 18:13:39 +0100
Subject: [PATCH 3/3] Following the advice of appgurueu, outsourced
 abundancyIndex ot its own function

---
 Maths/FriendlyNumbers.js | 33 ++++++++++++---------------------
 1 file changed, 12 insertions(+), 21 deletions(-)

diff --git a/Maths/FriendlyNumbers.js b/Maths/FriendlyNumbers.js
index 7ba69e90b3..a9b6b37ec9 100644
--- a/Maths/FriendlyNumbers.js
+++ b/Maths/FriendlyNumbers.js
@@ -14,28 +14,19 @@ export const FriendlyNumbers = (firstNumber, secondNumber) => {
     throw new Error('The two parameters must be distinct, non-null integers')
   }
 
-  // Calculate the abundancy index of the two number.
-  // ... first get the sum of their divisors
-  let sumDivisorsFirstNumber = firstNumber
-  let sumDivisorsSecondNumber = secondNumber
+  return abundancyIndex(firstNumber) === abundancyIndex(secondNumber)
+}
 
-  for (let i = 0; i < firstNumber / 2; i++) {
-    if (Number.isInteger(firstNumber / i)) {
-      sumDivisorsFirstNumber += i
-    }
-  }
-  for (let i = 0; i < secondNumber / 2; i++) {
-    if (Number.isInteger(secondNumber / i)) {
-      sumDivisorsSecondNumber += i
-    }
-  }
-  // ... and divide that sum by the number itself
-  const abundancyIndexFirstNumber = sumDivisorsFirstNumber / firstNumber
-  const abundancyIndexSecondNumber = sumDivisorsSecondNumber / secondNumber
+function abundancyIndex (number) {
+  return sumDivisors(number) / number
+}
 
-  if (abundancyIndexFirstNumber === abundancyIndexSecondNumber) {
-    return true
-  } else {
-    return false
+function sumDivisors (number) {
+  let runningSumDivisors = number
+  for (let i = 0; i < number / 2; i++) {
+    if (Number.isInteger(number / i)) {
+      runningSumDivisors += i
+    }
   }
+  return runningSumDivisors
 }