OraQA

The following is an interesting puzzle posted by mathpuzzle:

Multiples of single digits: The number 24 is the product of single digits, in two different ways: 4×6 or 3×8. 3256 has consecutive pairs 32, 25, 56, and each is the product of single digits (4×8, 5×5, and 7×8).

Arrange the digits of 1-9 so that every consecutive pair is the product of single digits.

—————-SQL solution—————————

SELECT to_number(replace(sys_connect_by_path( n,','),',')) num
FROM
(SELECT LEVEL n FROM dual CONNECT BY LEVEL <= 9)
 WHERE LEVEL = 9
 CONNECT BY NOCYCLE n != PRIOR n
 AND
 (    (mod(to_number( PRIOR N||N),9) = 0 AND to_number( PRIOR N||N)<= 9*9)
  OR (mod(to_number( PRIOR N||N),8) = 0 AND to_number( PRIOR N||N)<= 8*9)
  OR (mod(to_number( PRIOR N||N),7) = 0 AND to_number( PRIOR N||N)<= 7*9)
  OR (mod(to_number( PRIOR N||N),6) = 0 AND to_number( PRIOR N||N)<= 6*9)
  OR (mod(to_number( PRIOR N||N),5) = 0 AND to_number( PRIOR N||N)<= 5*9)
  OR (mod(to_number( PRIOR N||N),4) = 0 AND to_number( PRIOR N||N)<= 4*9)
  OR (mod(to_number( PRIOR N||N),3) = 0 AND to_number( PRIOR N||N)<= 3*9)
  OR (mod(to_number( PRIOR N||N),2) = 0 AND to_number( PRIOR N||N)<= 2*9)
 );

NUM
----------
 728163549

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