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 13:59, 4 July 2021
, 2 years agoAdded Forth solution
(Added Quackery.) |
(Added Forth solution) |
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167 179 181 191 199 311 313 337 347 353
359 373 383 389
</pre>
=={{header|Forth}}==
{{works with|Gforth}}
<lang forth>: prime? ( n -- ? ) here + c@ 0= ;
: not-prime! ( n -- ) here + 1 swap c! ;
: prime-sieve ( n -- )
here over erase
0 not-prime!
1 not-prime!
2
begin
2dup dup * >
while
dup prime? if
2dup dup * do
i not-prime!
dup +loop
then
1+
repeat
2drop ;
: reverse ( n -- n )
0 swap
begin
dup 0 >
while
10 /mod swap rot 10 * + swap
repeat drop ;
: main
1000 prime-sieve
0
500 1 do
i prime? if i reverse prime? if
1 +
i 3 .r
dup 10 mod 0= if cr else space then
then then
loop
cr ." Count: " . cr ;
main
bye</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
Count: 34
</pre>
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