Smarandache prime-digital sequence: Difference between revisions

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=={{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 + ;

: spds_print ( n -- )

0

begin

over 0 >

while

next_prime_digit_number

dup is_prime? if dup . swap 1- swap then

repeat

2drop cr ;

: spds_nth ( n -- n )

0

begin

over 0 >

while

next_prime_digit_number

dup is_prime? if swap 1- swap then

repeat

swap drop ;

." First 25 SPDS primes:" cr

25 spds_print

." 100th SPDS prime: "

100 spds_nth . cr

." 1000th SPDS prime: "

1000 spds_nth . cr</lang>

{{out}}

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First 25 SPDS primes:

2 3 5 7 23 37 53 73 223 227 233 257 277 337 353 373 523 557 577 727 733 757 773 2237 2273

100th SPDS prime: 33223

1000th SPDS prime: 3273527