Cousin primes: Difference between revisions
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967 971
Amount: 41</pre>
(In this example, we can get away with finding primes where adding 4 gives us another prime. But if the task had asked for cousin prime pairs less than 100, we would want to avoid the pair 97,101. And the simplest way of addressing that issue would have been to find primes where subtracting 4 gives us another prime.)
=={{header|jq}}==
Line 1,231 ⟶ 1,233:
41 pairs found.
</pre>
=={{header|Lua}}==
<syntaxhighlight lang="lua">
do -- find primes p where p+4 is also prime
local MAX_PRIME = 1000
local p = {} -- sieve the odd primes to MAX_PRIME
for i = 3, MAX_PRIME, 2 do p[ i ] = true end
for i = 3, math.floor( math.sqrt( MAX_PRIME ) ), 2 do
if p[ i ] then
for s = i * i, MAX_PRIME, i + i do p[ s ] = false end
end
end
local function fmt ( n ) return string.format( "%3d", n ) end
io.write( "Cousin primes under ", MAX_PRIME, ":\n" )
local cCount = 0
for i = 3, MAX_PRIME - 4, 2 do
if p[ i ] and p[ i + 4 ] then
cCount = cCount + 1
io.write( "[ ", fmt( i ), " ", fmt( i + 4 ), " ]"
, ( cCount % 8 == 0 and "\n" or " " )
)
end
end
io.write( "\nFound ", cCount, " cousin primes\n" )
end
</syntaxhighlight>
{{out}}
<pre>
Cousin primes under 1000:
[ 3 7 ] [ 7 11 ] [ 13 17 ] [ 19 23 ] [ 37 41 ] [ 43 47 ] [ 67 71 ] [ 79 83 ]
[ 97 101 ] [ 103 107 ] [ 109 113 ] [ 127 131 ] [ 163 167 ] [ 193 197 ] [ 223 227 ] [ 229 233 ]
[ 277 281 ] [ 307 311 ] [ 313 317 ] [ 349 353 ] [ 379 383 ] [ 397 401 ] [ 439 443 ] [ 457 461 ]
[ 463 467 ] [ 487 491 ] [ 499 503 ] [ 613 617 ] [ 643 647 ] [ 673 677 ] [ 739 743 ] [ 757 761 ]
[ 769 773 ] [ 823 827 ] [ 853 857 ] [ 859 863 ] [ 877 881 ] [ 883 887 ] [ 907 911 ] [ 937 941 ]
[ 967 971 ]
Found 41 cousin primes
</pre>
Line 1,820 ⟶ 1,859:
found 81 unique cousin primes.
done...
</pre>
=={{header|RPL}}==
{{works with|HP|49}}
≪ { } → cousins
≪ 2 3 5
'''DO'''
ROT DROP DUP NEXTPRIME
'''CASE'''
DUP 4 PICK - 4 == '''THEN''' PICK3 OVER R→C 'cousins' SWAP STO+ '''END'''
DUP2 - -4 == '''THEN''' DUP2 R→C 'cousins' SWAP STO+ '''END'''
'''END'''
'''UNTIL''' DUP 1000 ≥ '''END'''
3 DROPN
cousins DUP SIZE
≫ ≫ '<span style="color:blue">TASK</span>' STO
{{out}}
<pre>
2: { (3., 7.) (7., 11.) (13., 17.) (19., 23.) (37., 41.) (43., 47.) (67., 71.) (79., 83.) (97., 101.) (103., 107.) (109., 113.) (127., 131.) (163., 167.) (193., 197.) (223., 227.) (229., 233.) (277., 281.) (307., 311.) (313., 317.) (349., 353.) (379., 383.) (397., 401.) (439., 443.) (457., 461.) (463., 467.) (487., 491.) (499., 503.) (613., 617.) (643., 647.) (673., 677.) (739., 743.) (757., 761.) (769., 773.) (823., 827.) (853., 857.) (859., 863.) (877., 881.) (883., 887.) (907., 911.) (937., 941.) (967., 971.) }
1: 41
</pre>
Line 1,993 ⟶ 2,052:
{{libheader|Wren-math}}
{{libheader|Wren-fmt}}
<syntaxhighlight lang="
import "./fmt" for Fmt
var c = Int.primeSieve(999, false)
Line 2,022 ⟶ 2,081:
41 pairs found
</pre>
=={{header|XPL0}}==
<syntaxhighlight lang "XPL0">include xpllib; \For IsPrime and Print
int N, C;
[C:= 0;
for N:= 2 to 1000-1-4 do
[if IsPrime(N) then
if IsPrime(N+4) then
[Print("(%3.0f, %3.0f) ", float(N), float(N+4));
C:= C+1;
if rem(C/6) = 0 then CrLf(0);
];
];
Print("\nThere are %d cousin primes less than 1000.\n", C);
]</syntaxhighlight>
{{out}}
<pre>
( 3, 7) ( 7, 11) ( 13, 17) ( 19, 23) ( 37, 41) ( 43, 47)
( 67, 71) ( 79, 83) ( 97, 101) (103, 107) (109, 113) (127, 131)
(163, 167) (193, 197) (223, 227) (229, 233) (277, 281) (307, 311)
(313, 317) (349, 353) (379, 383) (397, 401) (439, 443) (457, 461)
(463, 467) (487, 491) (499, 503) (613, 617) (643, 647) (673, 677)
(739, 743) (757, 761) (769, 773) (823, 827) (853, 857) (859, 863)
(877, 881) (883, 887) (907, 911) (937, 941) (967, 971)
There are 41 cousin primes less than 1000.
</pre>
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