# What number goes in the ?? box?

A simple pattern puzzle

What is the number in the ?? box? Why? No programming please.

• I assume the off-by-one-error when trying the obvious solution is intentional? May 3, 2021 at 14:58
• Yep @Sleafar it is
– DrD
May 3, 2021 at 15:01

The missing number is

34

To get the value in a box from its two preceding inputs, you

take the product of all of the digits of each input, and then sum these together. For example, 3x6x6 + 2x4x2 = 108 + 16 = 124. To get the missing value, we see that 5x6 + 2x2 = 30 + 4 = 34.

• So wjy not "Clear the least signifcant bit and take the difference"? Gives the exact same result and is arguably simpler. May 4, 2021 at 3:55
• @loopywalt I'd say "Clear the least signifcant bit" is an extra rule and making an exception for only one number to make it fit, which is 'ugly'. The accepted answer has one rule that fits all. Also, it seems clear to me that something completely different for the almost matching 'difference' rule is sought. May 4, 2021 at 9:10
• I checked with my six year old and he didn't agree that "clear the least significant bit" was simpler. May 4, 2021 at 13:17
• My six year old stands by his statement. There's nothing simpler about your proposed alternate solution. May 4, 2021 at 13:49
• Actually, I'd like to apologise. For some reason this kind of puzzle never fails to annoy the sh** out of me. But obviously there is no point in being so negative/smart-arse/judgemental about what's after all just a bit of fun. May 4, 2021 at 14:05