DS4 randomly decided to write a number pattern (he originally said he wanted to count by 1's, 2's, 3's, 4's, etc...which I thought meant he was just going to skip-count, starting back at the beginning each time he changed to a new increment) -- but instead, it went like this:

1 2 3 4 6 8 10 12 15 18 21 24 28 32 36 40 45 50 55 60 66 72 78 84 91 98 105
112 120 128 136 144 153 162 171 180 190 200 210 220 231 242 253 264 276...

(in case you don't want to figure it out, it's four steps of each increment: counting by 1's four times, 2's four times, etc etc.) This alone was pretty cool, until he pointed out that he would end on a multiple of the next increment every time. (so at the end of the 5's he ends with a number divisible by 6 and so on and so forth.) The pattern doesn't stop. It took DH (super gifted in math) like 15 mins to figure out why. (if you are interested, it's because you end up with 4 x the successive triangle numbers, or 2n(n-1). and if you need more explanation than that, you'll have to ask DH because honestly, it's all lost on me!) But yeah, it was just...kind of mind-blowing that he was just able to toss that off.