Special neighbor primes: Difference between revisions

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{{Draft task}}
{{Draft task}}


;Task:Let &nbsp; ('''p<sub>1</sub>''', &nbsp;'''p<sub>2</sub>''') &nbsp; are neighbour primes. Find and show here in base ten if '''p<sub>1</sub>+&nbsp;p<sub>2</sub> &nbsp;-1''' is prime &nbsp; where &nbsp; '''p<sub>1</sub>, &nbsp; p<sub>2</sub> &nbsp;&lt;&nbsp; 100'''.
;Task:Let &nbsp; ('''p<sub>1</sub>''', &nbsp;'''p<sub>2</sub>''') &nbsp; are neighbour primes. Find and show here in base ten if '''p<sub>1</sub>+&nbsp;p<sub>2</sub>&nbsp;-1''' is prime &nbsp; where &nbsp; '''p<sub>1</sub>, &nbsp; p<sub>2</sub> &nbsp;&lt;&nbsp; 100'''.


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Revision as of 04:58, 6 August 2021

Special neighbor primes is a draft programming task. It is not yet considered ready to be promoted as a complete task, for reasons that should be found in its talk page.
Task
Let   (p1,  p2)   are neighbour primes. Find and show here in base ten if p1+ p2 -1 is prime   where   p1,   p2  <  100.



Ring

<lang ring> load "stdlib.ring"

see "working..." + nl see "Special neighbour primes are:" + nl row = 0 oldPrime = 2

for n = 3 to 100

   if isprime(n) and isprime(oldPrime) 
      sum = oldPrime + n - 1
      if isprime(sum)
         row++
         see "" + oldPrime + "," + n + " => " + sum + nl
      ok
      oldPrime = n
   ok

next

see "Found " + row + " special neighbour primes" see "done..." + nl </lang>

Output:
working...
Special twin primes are:
3,5 => 7
5,7 => 11
7,11 => 17
11,13 => 23
13,17 => 29
19,23 => 41
29,31 => 59
31,37 => 67
41,43 => 83
43,47 => 89
61,67 => 127
67,71 => 137
73,79 => 151
Found 13 special twin primesdone...