Primes whose first and last number is 3: Difference between revisions

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call genP /*build array of semaphores for primes.*/

w= 10 /*width of a number in any column. */

title= ' primes N (in base ten) that have a leading and ~~ending~~ digit of ' ~~dig~~ ,

title= ' primes N (in base ten) that have a leading and trailing digit of ' dig ,

" where N < " commas(hi)

if cols>0 then say ' index │'center(title, 1 + cols*(w+1) )

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if Td\==dig then iterate /* " " " " trailing ? ? */ /* ◄■■■■■■■ a filter.*/

found= found + 1 /*bump the number of primes found. */

if cols<= then iterate /*Build the list (to be shown later)? */

if cols<=0 then iterate /*Build the list (to be shown later)? */

c= commas(@.j) /*maybe add commas to the number. */

$= $ right(c, max(w, length(c) ) ) /*add a prime ──► $ list, allow big #*/

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<pre>

index │ primes N (in base ten) that have a leading and ~~ending~~ digit of 3 where N < 4,000

index │ primes N (in base ten) that have a leading and trailing digit of 3 where N < 4,000

───────┼───────────────────────────────────────────────────────────────────────────────────────────────────────────────

1 │ 3 313 353 373 383 3,023 3,083 3,163 3,203 3,253

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───────┴───────────────────────────────────────────────────────────────────────────────────────────────────────────────

Found 33 primes N (in base ten) that have a leading and ~~ending~~ digit of 3 where N < 4,000

Found 33 primes N (in base ten) that have a leading and trailing digit of 3 where N < 4,000

</pre>

{{out|output|text=  when using the default inputs of:     <tt> 1000000   -1 </tt>}}

<pre>

Found 2,251 primes N (in base ten) that have a leading and ~~ending~~ digit of 3 where N < 1,000,000

Found 2,251 primes N (in base ten) that have a leading and trailing digit of 3 where N < 1,000,000

</pre>