Neighbour primes
Neighbour 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
Find and show primes p such that p*q+2 is prime, where q is next prime after p, where p < 500
Ring
<lang ring> load "stdlib.ring" see "working..." + nl see "prime1 prime2 prime3" + nl
num = 0 pr = 0 limit = 100 Primes = []
while true
pr = pr + 1 if isprime(pr) add(Primes,pr) num = num + 1 if num = limit exit ok ok
end
for n = 1 to limit-1
prim = Primes[n]*Primes[n+1]+2 if isprime(prim) see "" + Primes[n] + " " + Primes[n+1] + " " + prim + nl ok
next
see "done..." + nl </lang>
- Output:
working... prime1 prime2 prime3 3 5 17 5 7 37 7 11 79 13 17 223 19 23 439 67 71 4759 149 151 22501 179 181 32401 229 233 53359 239 241 57601 241 251 60493 269 271 72901 277 281 77839 307 311 95479 313 317 99223 397 401 159199 401 409 164011 419 421 176401 439 443 194479 487 491 239119 done...