12, 33, 66, 132, 363, _____ 

1. Each number in the sequence undergoes a transformation involving reversing the digits of the number and then adding the original number to this reversed number:
   • 12: Reverse it to 21, add 12 + 21 = 33.
   • 33: Reverse it to 33, add 33 + 33 = 66.
   • 66: Reverse it to 66, add 66 + 66 = 132.
   • 132: Reverse it to 231, add 132 + 231 = 363.
   • 363: Reverse it to 363, add 363 + 363 = 726.

So, the next number in the sequence after 363 is 726.