I also likes the table of 37, but this works better for smaller numbers. This gives: 37 x 115 -> 37 x 3 + (114 / 3) + 37. I know that 37x3=111. With some efforts, I can see that 114 / 3 -> 38. I am still memory free to perform the difficult 111x38 -> 3800+380+38 = 4180+38 = 4218 that I pain to remember to add 37. In this case, the table of 37 is not very effective.