Mental Math

Drills at a digit count and operation set you pick, and division always comes out even.

equations.arithmetic · v1 · renderer math

1. 98 - 55 → 43 2. 99*4 → 396 3. 62*3 → 186 4. 357/7 → 51 5. 88 - 30 → 58 6. 46*4 → 184 7. 63*7 → 441 8. 59 - 41 → 18 9. 97 - 63 → 34 10. 26*2 → 52

entropy in

16 bytes

stream used

34 bytes

rejections

duration

388 µs

problems

Seed receipt

Class C · Observational

Planetary K-index 0.67 — the geomagnetic field was quiet when this was made.

Carries only tens of bits of genuine surprise. Always mixed with the OS CSPRNG.

source: NOAA Space Weather
observed: 2026-09-13T18:37:00+00:00
latency: 275ms
mixed with: csprng — always

https://www.swpc.noaa.gov/products/planetary-k-index ↗

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The token is the seed, so this link recomputes the result rather than looking it up. No database, and it works for as long as v1 does.

Controls · from schema()

Operations

Digits

1 4

How large the operands get.

How many

1 100

Allow negatives

Lets a subtraction go below zero, and operands turn negative.

Entropy source

Picking a source changes the story on the receipt, never the quality: anything below class A is mixed with the OS CSPRNG before it reaches you. This result actually came from NOAA Space Weather.

seed token PQWF0PX9YAKV6M8WT2FJ92KWAM

Re-render keeps this token. Generate replaces it. That is the whole idea.

Printable worksheet 20 problems · answers on page 2

The seed is printed in the footer, so the same sheet comes back from the same link — and a different seed is a different sheet.

This page and /api/v1/g/equations.arithmetic run the same code. There is no private endpoint.

Mental Math

Result

Measurements

Seed receipt

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