Perfect numbers: Difference between revisions
Added Wren
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(Added Wren) |
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=={{header|Wren}}==
===Version 1===
{{trans|D}}
Restricted to the first four perfect numbers as the fifth one is very slow to emerge.
<lang ecmascript>var isPerfect = Fn.new { |n|
if (n <= 2) return false
var tot = 1
for (i in 2..n.sqrt.floor) {
if (n%i == 0) {
tot = tot + i
var q = (n/i).floor
if (q > i) tot = tot + q
}
}
return n == tot
}
System.print("The first four perfect numbers are:")
var count = 0
var i = 2
while (count < 4) {
if (isPerfect.call(i)) {
System.write("%(i) ")
count = count + 1
}
i = i + 2 // there are no known odd perfect numbers
}
System.print()</lang>
{{out}}
<pre>
6 28 496 8128
</pre>
===Version 2===
This makes use of the fact that all known perfect numbers are of the form <big> (2<sup>''n''</sup> - 1) × 2<sup>''n'' - 1</sup></big> where <big> (2<sup>''n''</sup> - 1)</big> is prime and finds the first seven perfect numbers instantly. The numbers are too big after that to be represented accurately by Wren.
<lang ecmascript>var isPrime = Fn.new { |n|
if (n < 2 || !n.isInteger) return false
if (n%2 == 0) return n == 2
if (n%3 == 0) return n == 3
var d = 5
while (d*d <= n) {
if (n%d == 0) return false
d = d + 2
if (n%d == 0) return false
d = d + 4
}
return true
}
var isPerfect = Fn.new { |n|
if (n <= 2) return false
var tot = 1
for (i in 2..n.sqrt.floor) {
if (n%i == 0) {
tot = tot + i
var q = (n/i).floor
if (q > i) tot = tot + q
}
}
return n == tot
}
System.print("The first seven perfect numbers are:")
var count = 0
var p = 2
while (count < 7) {
var n = 2.pow(p) - 1
if (isPrime.call(n)) {
n = n * 2.pow(p-1)
if (isPerfect.call(n)) {
System.write("%(n) ")
count = count + 1
}
}
p = p + 1
}
System.print()</lang>
{{out}}
<pre>
6 28 496 8128 33550336 8589869056 137438691328
</pre>
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