Concatenate two primes is also prime: Difference between revisions

=={{header|Go}}==

{{libheader|Go-rcu}}

<lang go>package main

import (

"fmt"

"rcu"

"sort"

)

func main() {

const LIMIT = 99

primes := rcu.Primes(LIMIT)

rmap := make(map[int]bool)

for _, p := range primes {

for _, q := range primes {

var pq int

if q < 10 {

pq = p*10 + q

} else {

pq = p*100 + q

}

if rcu.IsPrime(pq) {

rmap[pq] = true

}

}

}

results := make([]int, len(rmap))

i := 0

for k := range rmap {

results[i] = k

i++

}

sort.Ints(results)

fmt.Println("Two primes under 100 concatenated together to form another prime:")

for i, p := range results {

fmt.Printf("%5s ", rcu.Commatize(p))

if (i+1)%10 == 0 {

fmt.Println()

}

}

fmt.Println("\n\nFound", len(results), "such concatenated primes.")

}</lang>

{{out}}

<pre>

Two primes under 100 concatenated together to form another prime:

23 37 53 73 113 137 173 193 197 211

223 229 233 241 271 283 293 311 313 317

331 337 347 353 359 367 373 379 383 389

397 433 523 541 547 571 593 613 617 673

677 719 733 743 761 773 797 977 1,117 1,123

1,129 1,153 1,171 1,319 1,361 1,367 1,373 1,723 1,741 1,747

1,753 1,759 1,783 1,789 1,913 1,931 1,973 1,979 1,997 2,311

2,341 2,347 2,371 2,383 2,389 2,917 2,953 2,971 3,119 3,137

3,167 3,719 3,761 3,767 3,779 3,797 4,111 4,129 4,153 4,159

4,337 4,373 4,397 4,723 4,729 4,759 4,783 4,789 5,323 5,347

5,923 5,953 6,113 6,131 6,143 6,173 6,197 6,719 6,737 6,761

6,779 7,129 7,159 7,331 7,919 7,937 8,311 8,317 8,329 8,353

8,389 8,923 8,929 8,941 8,971 9,719 9,743 9,767

Found 128 such concatenated primes.

</pre>