# Sudoku Odd Pairs – a new variant!

Now here’s something I can guarantee you won’t have seen before, because I just invented it! Well, I suppose with a world of people creating Sudoku variants it’s possible there’s been something similar before, but I’ve bought a *lot* of puzzle magazines and books and never come across it, so perhaps I should say I can *just about* guarantee you won’t have seen it before!

So the puzzle is **Sudoku Odd Pairs**, and as the name implies it’s all about odd pairs of numbers. Now you may have come across regular odd/even Sudoku before, and to be honest it’s a pretty dull variant (which is why I’ve never made them) – in fact if you for example shade all squares that contain even numbers it just breaks into two separate puzzles that overlap, and if you instead mark just a selection of even (or odd) squares then it’s only interesting until you work out whether the shaded squares are odd or even.

**Sudoku Odd Pairs** isn’t like that, because instead of marking squares what I’ve done is mark *pairs *of squares. Some squares have a grey circle between them – you can think of this as an **O **for **O**dd. What this means is that the *sum* of the solution of these two squares is odd. I don’t mark *all* odd pairs, however, because if you do this you need only one single digit in the entire grid (any of the givens will do) to work out which squares are odd and which even and then you end up with the above boring variant again. So this is important:* *you can’t infer anything about squares *without* an **O** between them – only those *with *the **O **between.

It turns out (at least in my opinion!) that this is actually a really fun variant, because you end up with many interesting parts of each puzzle where you realise you can force sets of odds or evens into groups of squares (and not just those with the **O**s on), which in turn effect the rest of the puzzle. You do to an extent need to make pencil marks when solving, as in Consecutive and many other variants, *but* the nature of the constraint is such that the number of pencil marks is roughly halved relative to most other variants which (for me at least) makes it far more fun.

I’ve talked about it enough. Try out the puzzle here and let me know what you think!

And if you would like more of these, I’m putting them into Sudoku Xtra issue 4 (out soon!), including a nice Samurai version.

about 11 years ago

Very cool puzzle Gareth! I’ll give it a try shortly. I may have to try my hand at including this variant in one of my trickle-down sudoku sheets next time I make one…

Spittledungabout 11 years ago

Interesting idea Gareth. The rules remind of the classic dice game “Can’t Stop”.

So going on from what you have told us:

1. The only way for the sum to be odd is if one of the numbers next to the O is odd and the other is even.

2. There are 5 odd numbers and 4 even numbers per row/column/region. (As usual)

This 9×9 was enjoyable. Any bigger and it gets tedious for me (see other message )