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/*
* Check if the current number is prime
*/
CREATE OR REPLACE FUNCTION f_is_prime( n int )
RETURNS bool
AS $CODE$
DECLARE
divisor int;
BEGIN
FOR divisor IN 2 .. ( n - 1 ) LOOP
IF mod( n, divisor ) = 0 THEN
RETURN false;
END IF;
END LOOP;
RETURN TRUE;
END
$CODE$
LANGUAGE plpgsql;
CREATE OR REPLACE FUNCTION f_semiprime_factors( n int )
RETURNS SETOF int
AS $CODE$
DECLARE
current_number int;
BEGIN
FOR current_number IN 1 .. n LOOP
IF f_is_prime( current_number ) AND mod( n, current_number ) = 0 AND f_is_prime( ( n / current_number ) ) THEN
RETURN NEXT current_number;
END IF;
END LOOP;
RETURN;
END
$CODE$
LANGUAGE plpgsql;
CREATE OR REPLACE FUNCTION f_is_semiprime( n int )
RETURNS bool
AS $CODE$
SELECT CASE count( * )
WHEN 0 THEN false
ELSE true
END
FROM f_semiprime_factors( n ) s;
$CODE$
LANGUAGE sql;
CREATE OR REPLACE FUNCTION f_find_semiprimes( lim int default 100 )
RETURNS SETOF int
AS $CODE$
DECLARE
n int;
BEGIN
n := 1;
WHILE n < lim LOOP
IF f_is_semiprime( n ) THEN
RETURN NEXT n;
END IF;
n := n + 1;
END LOOP;
RETURN;
END
$CODE$
LANGUAGE plpgsql;
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