Way of Indian Math: Solve 87 × 13 in your head. In under 5 seconds.

Hey PH 👋 Quick story. In 2010 there was this Japanese app called Indian Calc Master, made by a small studio called PandraHouse. It taught you to do mental math the Vedic way — stuff like 87 × 13, in your head, in a few seconds. I was a kid when I downloaded it. It wrecked my brain in the best way. I'd do problems at the dinner table just to freak my parents out. The app's been gone for years. PandraHouse moved on, the App Store quietly buried it. I checked once a year for a while, then stopped. A few months ago I decided to just rebuild it. Same idea, same dojo feel, but rewritten from zero in Flutter, and translated into 6 languages so it's not only a Japanese thing anymore. It's called Way of Indian Math. The structure is basically the same as the original: 13 techniques, organized as a martial arts ranking. You start at 6th kyu and work your way up to 7th dan. Each belt teaches one specific trick — Nikhilam, Urdhva-Tiryagbhyam, the "tens-match, ones-complement" pattern, and so on. The end goal is solving any 2-digit × 2-digit problem in under 5 seconds. The Japanese name is 「インド式計算道」, "the way of Indian calculation". 道 (dō) is the same one in 柔道 / 書道 / 茶道. The idea is that this isn't a feature, it's a practice. A few choices that mattered to me: - One-time $3. No ads, no subscription, no signup. Buy it, it's yours. - Six languages from day one: English, Japanese, Korean, Chinese, French, Spanish. - Ganesha is still the mascot. The technique is Indian, the original had him, felt wrong to drop him. - Fully offline. Nothing leaves the device. Safe to hand to a kid. I made it on nights and weekends, mostly solo, with a lot of help from Claude Code. Stuff I'd actually like your honest read on: 1. Does the kyu/dan progression make sense outside Japan, or does it just feel weird? 2. $3 once, or do people on PH expect free + ads now? 3. If your kid (or you) tried this for a week, what would actually make you keep coming back? If you've got a minute, jump straight to 7th dan and try a generic ab × cd problem cold. Tell me your time, and whether you wanted to throw your phone. I'll be in the comments all day. — hiro960