Next special primes
- Task
n is smallest prime such that the difference of successive terms is strictly increasing,
where n < 1050.
Pascal
just showing the small difference to increasing prime gaps.
LastPrime is updated outside or inside If
<lang pascal> program NextSpecialprimes; //increasing prime gaps see //https://oeis.org/A002386 https://en.wikipedia.org/wiki/Prime_gap uses
sysutils, primTrial;
procedure GetIncreasingGaps; var
Gap,LastPrime,p : NativeUInt;
Begin
InitPrime;
Writeln('next increasing prime gap');
writeln('Prime1':8,'Prime2':8,'Gap':4);
Gap := 0;
LastPrime := actPrime;
repeat
p := NextPrime;
if p-LastPrime > Gap then
Begin
Gap := p-LastPrime;
writeln(LastPrime:8,P:8,Gap:4);
end; LastPrime := p; until LastPrime > 1000;
end;
procedure NextSpecial; var
Gap,LastPrime,p : NativeUInt;
Begin
InitPrime;
Writeln('next special prime');
writeln('Prime1':8,'Prime2':8,'Gap':4);
Gap := 0;
LastPrime := actPrime;
repeat
p := NextPrime;
if p-LastPrime > Gap then
Begin
Gap := p-LastPrime;
writeln(LastPrime:8,P:8,Gap:4);
LastPrime := p;
end;
until LastPrime > 1000;
end;
begin
GetIncreasingGaps; writeln; NextSpecial;
end.</lang>
- Output:
next increasing prime gap
Prime1 Prime2 Gap
2 3 1
3 5 2
7 11 4
23 29 6
89 97 8
113 127 14
523 541 18
887 907 20
next special prime
Prime1 Prime2 Gap
2 3 1
3 5 2
5 11 6
11 19 8
19 29 10
29 41 12
41 59 18
59 79 20
79 101 22
101 127 26
127 157 30
157 191 34
191 227 36
227 269 42
269 313 44
313 359 46
359 409 50
409 461 52
461 521 60
521 587 66
587 659 72
659 733 74
733 809 76
809 887 78
887 967 80
967 1049 82
REXX
<lang rexx>/*REXX program finds next special primes: difference of successive terms is increasing.*/ parse arg hi cols . /*obtain optional argument from the CL.*/ if hi== | hi=="," then hi= 1050 /* " " " " " " */ if cols== | cols=="," then cols= 10 /* " " " " " " */ call genP /*build array of semaphores for primes.*/ w= 10 /*width of a number in any column. */
@nsp= ' next special primes < ' commas(hi) ,
" such that the different of successive terms is increasing"
if cols>0 then say ' index │'center(@nsp , 1 + cols*(w+1) ) if cols>0 then say '───────┼'center("" , 1 + cols*(w+1), '─') op= @.1 /*assign oldPrime to the first prime.*/ nsp= 0; idx= 1 /*initialize number of nsp and index.*/ $= /*a list of nice primes (so far). */
do j=0; np= op + j /*assign newPrime to oldPrime + j */
if np>=hi then leave /*Is newPrimeN ≥ hi? Then leave loop.*/
if \!.np then iterate /*Is np a prime? Then skip this J.*/
nsp= nsp + 1 /*bump the number of nsp's. */
op= np /*set oldPrime to the value of newPrime*/
if cols==0 then iterate /*Build the list (to be shown later)? */
c= commas(np) /*maybe add commas to the number. */
$= $ right(c, max(w, length(c) ) ) /*add a nice prime ──► list, allow big#*/
if nsp//cols\==0 then iterate /*have we populated a line of output? */
say center(idx, 7)'│' substr($, 2); $= /*display what we have so far (cols). */
idx= idx + cols /*bump the index count for the output*/
end /*j*/
if $\== then say center(idx, 7)"│" substr($, 2) /*possible display residual output.*/ say say 'Found ' commas(nsp) @nsp exit 0 /*stick a fork in it, we're all done. */ /*──────────────────────────────────────────────────────────────────────────────────────*/ commas: parse arg ?; do jc=length(?)-3 to 1 by -3; ?=insert(',', ?, jc); end; return ? /*──────────────────────────────────────────────────────────────────────────────────────*/ genP: !.= 0 /*placeholders for primes (semaphores).*/
@.1=2; @.2=3; @.3=5; @.4=7; @.5=11 /*define some low primes. */
!.2=1; !.3=1; !.5=1; !.7=1; !.11=1 /* " " " " flags. */
#=5; s.#= @.# **2 /*number of primes so far; prime². */
/* [↓] generate more primes ≤ high.*/
do j=@.#+2 by 2 to hi /*find odd primes from here on. */
parse var j -1 _; if _==5 then iterate /*J divisible by 5? (right dig)*/
if j// 3==0 then iterate /*" " " 3? */
if j// 7==0 then iterate /*" " " 7? */
/* [↑] the above five lines saves time*/
do k=5 while s.k<=j /* [↓] divide by the known odd primes.*/
if j // @.k == 0 then iterate j /*Is J ÷ X? Then not prime. ___ */
end /*k*/ /* [↑] only process numbers ≤ √ J */
#= #+1; @.#= j; s.#= j*j; !.j= 1 /*bump # of Ps; assign next P; P²; P# */
end /*j*/; return</lang>
- output when using the default inputs:
index │ next special primes < 1,050 such that the different of successive terms is increasing ───────┼─────────────────────────────────────────────────────────────────────────────────────────────────────────────── 1 │ 2 3 5 11 19 29 41 59 79 101 11 │ 127 157 191 227 269 313 359 409 461 521 21 │ 587 659 733 809 887 967 1,049 Found 27 next special primes < 1,050 such that the different of successive terms is increasing
Ring
<lang ring> load "stdlib.ring"
see "working..." + nl
Primes = [] limit1 = 100 oldPrime = 2
for n = 1 to limit1
nextPrime = oldPrime + n
if isprime(nextPrime)
add(Primes,nextPrime)
oldPrime = nextPrime
ok
next
see "prime1 prime2 Gap" + nl for n = 1 to Len(Primes)-1 step 2
diff = Primes[n+1] - Primes[n] see ""+ Primes[n] + " " + Primes[n+1] + " " + diff + nl
next
see nl + "done..." + nl
</lang>
- Output:
working... prime1 prime2 Gap 3 5 2 11 19 8 29 41 12 59 79 20 101 127 26 157 191 34 227 269 42 313 359 46 409 461 52 521 587 66 659 733 74 809 887 78 967 1049 82 done...