Cousin primes: Difference between revisions
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There are 41 cousin prime pairs below 1000.</pre>
=={{header|COBOL}}==
<lang cobol> IDENTIFICATION DIVISION.
PROGRAM-ID. COUSIN-PRIMES.
DATA DIVISION.
WORKING-STORAGE SECTION.
01 PRIME-SIEVE.
02 PRIME-FLAG PIC 9 OCCURS 1000 INDEXED BY P, Q.
88 PRIME VALUE 1.
02 STEP-SIZE PIC 999.
02 X PIC 999.
02 P-START PIC 999.
02 AMOUNT PIC 999 VALUE 0.
01 OUTPUT-FORMAT.
02 COUSIN1 PIC ZZ9.
02 COUSIN2 PIC ZZ9.
PROCEDURE DIVISION.
BEGIN.
PERFORM SIEVE.
PERFORM TEST-COUSINS VARYING P FROM 2 BY 1
UNTIL P IS GREATER THAN 996.
MOVE AMOUNT TO COUSIN1.
DISPLAY COUSIN1 ' pairs found.'
STOP RUN.
TEST-COUSINS.
IF PRIME(P) AND PRIME(P + 4)
SET X TO P
MOVE X TO COUSIN1
ADD X, 4 GIVING COUSIN2
DISPLAY COUSIN1 ' ' COUSIN2
ADD 1 TO AMOUNT.
SIEVE SECTION.
BEGIN.
PERFORM FLAG-PRIME VARYING Q FROM 1 BY 1
UNTIL Q IS GREATER THAN 1000.
PERFORM SIEVE-PRIME VARYING P FROM 2 BY 1
UNTIL P IS GREATER THAN 32.
GO TO DONE.
SIEVE-PRIME.
IF PRIME(P)
SET X TO P
COMPUTE P-START = X ** 2
PERFORM UNFLAG-PRIME VARYING Q FROM P-START BY X
UNTIL Q IS GREATER THAN 1000.
FLAG-PRIME. MOVE 1 TO PRIME-FLAG(Q).
UNFLAG-PRIME. MOVE 0 TO PRIME-FLAG(Q).
DONE. EXIT.</lang>
{{out}}
<pre style='height:14em;'> 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
41 pairs found.</pre>
=={{header|Cowgol}}==
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