Posted 03 July 2007 - 04:31 PM
last two digits cannot end in a 0 (all multiples will have a zero in them, thus 10, 20, 30, ... 80, 90 not the last two digits) [removes 30 from your list]
last two digits must be less than 33 (to satisfy 1 and 4)
last two digits cannot be adjacent, nor both even (from 2) [removes 14]
last two digits cannot have multiples less than 100 whose digits are adjacent [removes 27, 29 from your list]
last two digits cannot have a 5 in it (05 and 25 removed - no pair of multiples lack both 5 and 0)
last two digits cannot have multiples comprised only of even digits [removes 16]
03, 07, 09, 18 remain
03 can use the following multiples: 15, 18, 27, 69, 81
07 can use the following multiples: 49, 63, 91
09 can use the following multiples: 18, 27, 36, 63, 72, 81
18 can use the following multiples: 36, 72, 90
example: pick a number ending in "07" and use 49 and 63 gives us 496307 or 634907
However, because of the different rules, not every combination is allowed
03 only has 9 possible combinations
07 only has 2 possible combinations
09 only has 17 possible combinations
18 only has 6 possible combinations
Thus, I believer there to be only 29 different cyphers possible, according to the stated boundary conditions.