Double Twin Primes: Difference between revisions

Reusing some code from the [[Successive prime differences#ALGOL_68|Successive prime differences task]].

{{libheader|ALGOL 68-rows}}

PR read "rows.incl.a68" PR # include row (array) utilities #

# attempts to find patterns in the differences of primes and prints the results #

PROC try differences = ( []INT primes, []INT pattern, INT max prime )VOID:

BEGIN

INT pattern length = ( UPB pattern - LWB pattern ) + 1;

[ 1 : pattern length + 1 ]INT first; FOR i TO UPB first DO first[ i ] := 0 OD;

[ 1 : pattern length + 1 ]INT last; FOR i TO UPB last DO last[ i ] := 0 OD;

INT count := 0;

FOR p FROM LWB primes + pattern length TO UPB primes DO

BOOL matched := TRUE;

INT e pos := LWB pattern;

FOR e FROM p - pattern length TO p - 1

WHILE matched := primes[ e + 1 ] - primes[ e ] = pattern[ e pos ]

DO

e pos +:= 1

OD;

IF matched THEN

# found a matching sequence #

count +:= 1;

print( ( "[" ) );

SHOW primes[ p - pattern length : p ];

print( ( " ]", newline ) )

OD;

print( ( "Found ", whole( count, 0 ), " prime sequences with differences: [" ) );

SHOW pattern;

print( ( " ] up to ", whole( max prime, 0 ) ) );

print( ( newline ) )

END # try differences # ;

INT max number = 1 000;

[]INT p list = EXTRACTPRIMESUPTO max number FROMPRIMESIEVE PRIMESIEVE max number;

try differences( p list, ( 2, 4, 2 ), max number )

[ 5 7 11 13 ]

[ 11 13 17 19 ]

Found 5 prime sequences with differences: [ 2 4 2 ] up to 1000