Find prime n such that reversed n is also prime: Difference between revisions
Find prime n such that reversed n is also prime (view source)
Revision as of 00:22, 29 March 2021
, 3 years ago→{{header|ALGOL W}}
(julia example) |
Catskill549 (talk | contribs) |
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Found 34 reversable primes below 500
</pre>
=={{header|AWK}}==
<lang AWK>
# syntax: GAWK -f FIND_PRIME_N_FOR_THAT_REVERSED_N_IS_ALSO_PRIME.AWK
BEGIN {
start = 1
stop = 500
for (i=start; i<=stop; i++) {
if (is_prime(i) && is_prime(revstr(i,length(i)))) {
printf("%3d%1s",i,++count%10?"":"\n")
}
}
printf("\nReversible 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)
}
function revstr(str,start) {
if (start == 0) {
return("")
}
return( substr(str,start,1) revstr(str,start-1) )
}
</lang>
{{out}}
<pre>
2 3 5 7 11 13 17 31 37 71
73 79 97 101 107 113 131 149 151 157
167 179 181 191 199 311 313 337 347 353
359 373 383 389
Reversible primes 1-500: 34
</pre>
=={{header|Delphi}}==
{{libheader| System.SysUtils}}
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