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Added a new Maths algorithm to determine if two non-null integers are "friendly numbers" (TheAlgorithms#1267)

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	`1`	`+/*`
	`2`	`+ 'In number theory, friendly numbers are two or more natural numbers with a common abundancy index, the`
	`3`	`+ ratio between the sum of divisors of a number and the number itself.'`
	`4`	`+ Source: https://en.wikipedia.org/wiki/Friendly_number`
	`5`	`+ See also: https://mathworld.wolfram.com/FriendlyNumber.html#:~:text=The%20numbers%20known%20to%20be,numbers%20have%20a%20positive%20density.`
	`6`	`+*/`
	`7`	`+`
	`8`	`+exportconstFriendlyNumbers=(firstNumber,secondNumber)=>{`
	`9`	`+// input: two integers`
	`10`	`+// output: true if the two integers are friendly numbers, false if they are not friendly numbers`
	`11`	`+`
	`12`	`+// First, check that the parameters are valid`
	`13`	`+if(!Number.isInteger(firstNumber)\|\|!Number.isInteger(secondNumber)\|\|firstNumber===0\|\|secondNumber===0\|\|firstNumber===secondNumber){`
	`14`	`+thrownewError('The two parameters must be distinct, non-null integers')`
	`15`	`+}`
	`16`	`+`
	`17`	`+returnabundancyIndex(firstNumber)===abundancyIndex(secondNumber)`
	`18`	`+}`
	`19`	`+`
	`20`	`+functionabundancyIndex(number){`
	`21`	`+returnsumDivisors(number)/number`
	`22`	`+}`
	`23`	`+`
	`24`	`+functionsumDivisors(number){`
	`25`	`+letrunningSumDivisors=number`
	`26`	`+for(leti=0;i<number/2;i++){`
	`27`	`+if(Number.isInteger(number/i)){`
	`28`	`+runningSumDivisors+=i`
	`29`	`+}`
	`30`	`+}`
	`31`	`+returnrunningSumDivisors`
	`32`	`+}`

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