Use Hi-Lo lite count per half decks remaining, or Hi-Lo count per decks remaining with rounded indices. It's been known for quite some time that rounding indices properly doesn't affect performance materially.
All indices for Hi-Lo lite are +-2,4, and 0. Hi-Lo and RPC (count per half decks remaining) also perform well with rounded indices to +-4,8, and 0, with the one exception being 12 vs. 3 at +2, sims a bit better.
If you do this it becomes much easier to memorize many indices. For example with Hi-Lo lite 12 vs. 3,4,5,6 (S17) are 0. 13 vs. 2,3 are 0. 16 vs. 9, 15 vs. 10 are 2, etc...
Becomes much easier to recall the index. Just thinking 0,+-2 and occasionally +-4.