Twin primes: Difference between revisions
→{{header|ALGOL 68}}
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Maximum: 10000000
twin prime pairs below 10000000: 58980
</pre>
=={{header|AWK}}==
<lang AWK>
# syntax: GAWK -f TWIN_PRIMES.AWK
BEGIN {
n = 1
for (i=1; i<=6; i++) {
n *= 10
printf("twin prime pairs < %8s : %d\n",n,count_twin_primes(n))
}
exit(0)
}
function count_twin_primes(limit, count,i,p1,p2,p3) {
p1 = 0
p2 = p3 = 1
for (i=5; i<=limit; i++) {
p3 = p2
p2 = p1
p1 = is_prime(i)
if (p3 && p1) {
count++
}
}
return(count)
}
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>
twin prime pairs < 10 : 2
twin prime pairs < 100 : 8
twin prime pairs < 1000 : 35
twin prime pairs < 10000 : 205
twin prime pairs < 100000 : 1224
twin prime pairs < 1000000 : 8169
</pre>
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