Neighbour primes: Difference between revisions
added AWK
(Added C# version, showing totals for some other offsets.) |
Catskill549 (talk | contribs) (added AWK) |
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3 5 7 13 19 67 149 179 229 239 241 269 277 307 313 397 401 419 439 487
Found 20 neighbour primes up to 500
</pre>
=={{header|AWK}}==
<lang AWK>
# syntax: GAWK -f NEIGHBOUR_PRIMES.AWK
BEGIN {
print(" p q p*q+2")
print("---- ---- ------")
start = 1
stop = 499
for (p=start; p<=stop; p++) {
if (!is_prime(p)) { continue }
q = p + 1
while (!is_prime(q)) {
q++
}
if (!is_prime(p*q+2)) { continue }
printf("%4d %4d %6d\n",p,q,p*q+2)
count++
}
printf("Neighbour primes %d-%d: %d\n",start,stop,count)
exit(0)
}
function is_prime(x, i) {
if (x <= 1) {
return(0)
}
for (i=2; i<=int(sqrt(x)); i++) {
if (x % i == 0) {
return(0)
}
}
return(1)
}
</lang>
{{out}}
<pre>
p q p*q+2
---- ---- ------
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
Neighbour primes 1-499: 20
</pre>
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