Ultra useful primes: Difference between revisions

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 =={{header|Wren}}==
+===CLI===
-{{libheader|Wren-gmp}}
+{{libheader|Wren-big}}
-An embedded version as Wren-CLI (with BigInt) will be very slow for this task.
+{{libheader|Wren-fmt}}
+Manages to find the first ten but takes 84 seconds to do so.
+<lang ecmascript>import "./big" for BigInt
+import "./fmt" for Fmt
+var one = BigInt.one
-The following takes about 17.5 seconds to get to n = 13 but 7 minutes 15 seconds to reach n = 14. I didn't bother after that.
+var two = BigInt.two
+var a = Fn.new { |n|
+    var p = (BigInt.one << (1 << n)) - one
+    var k = 1
+    while (true) {
+        if (p.isProbablePrime(5)) return k
+        p = p - two
+        k = k + 2
+    }
+}
+System.print(" n   k")
+System.print("----------")
+for (n in 1..10) Fmt.print("$2d   $d", n, a.call(n))</lang>
+{{out}}
+<pre>
+ n   k
+----------
+1
+3
+5
+15
+5
+59
+159
+189
+569
+105
+</pre>
+===Embedded===
+{{libheader|Wren-gmp}}
+The following takes about 17 seconds to get to n = 13 but 7 minutes 10 seconds to reach n = 14. I didn't bother after that.
 <lang ecmascript>import "./gmp" for Mpz
 import "./fmt" for Fmt
+var one = Mpz.one
+var two = Mpz.two
 var a = Fn.new { |n|
-    var p = Mpz.one.lsh(1 << n)
+    var p = Mpz.one.lsh(1 << n).sub(one)
     var k = 1
     while (true) {
-        var q = p - k
+        if (p.probPrime(15) > 0) return k
-        if (q.probPrime(15) > 0) return k
+        p.sub(two)
         k = k + 2
     }