Extra primes: Difference between revisions
Added Forth solution
(Added Forth solution) |
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</pre>
=={{header|Forth}}==
<lang forth>: is_prime? ( n -- flag )
dup 2 < if drop false exit then
dup 2 mod 0= if 2 = exit then
dup 3 mod 0= if 3 = exit then
5
begin
2dup dup * >=
while
2dup mod 0= if 2drop false exit then
2 +
2dup mod 0= if 2drop false exit then
4 +
repeat
2drop true ;
: next_prime_digit_number ( n -- n )
dup 0= if drop 2 exit then
dup 10 mod
dup 2 = if drop 1+ exit then
dup 3 = if drop 2 + exit then
dup 5 = if drop 2 + exit then
drop
10 / recurse 10 * 2 + ;
: digit_sum ( n -- n )
0
begin
over 0 >
while
over 10 mod +
swap 10 / swap
repeat
swap drop ;
: extra_primes ( n -- )
2
begin
2dup >
while
dup is_prime? if dup digit_sum is_prime? if dup . cr then then
next_prime_digit_number
repeat
2drop ;
." Extra primes under 10000:" cr
10000 extra_primes</lang>
{{out}}
<pre>
Extra primes under 10000:
2
3
5
7
23
223
227
337
353
373
557
577
733
757
773
2333
2357
2377
2557
2753
2777
3253
3257
3323
3527
3727
5233
5237
5273
5323
5527
7237
7253
7523
7723
7727
</pre>
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