Primality vs Momentous Clock
Price, ratings, monetisation and update history for both apps, side by side — with what reviewers say about each.
Primality
This app determines if a given integer is prime or provides its prime factors. It also calculates the ordinal position of prime numbers found, up to a certain limit.
- Primality testing
- Prime factorization
- Prime ordinality calculation
- Large integer support (up to 999,999,999,999)
- Clean and simple interface
Read full descriptionHide full description
The Primality App has a clean and simple, yet powerful, function: Given any integer, the app determines either that the given integer is prime or else it provides all prime factors of that integer. Very clean, very simple, focussed. The app operates in the range of 0 - 999,999,999,999. A popular feature of the app is its ability to determine the prime ordinality of each prime found, such as observing that 97 if the 25th prime. (However, this particular feature is available only up to the 100,000th prime, which is 1,299,709.) Requires iOS 13 or higher.
Momentous Clock
This app transforms your device's clock into a dynamic display of mathematical properties and number theory facts for the current time. It optionally reveals personal number connections from your contacts, all processed securely on your device.
- Computes mathematical properties of time
- Surfaces number theory facts
- Displays time on 16-segment LED screens
- Finds personal number connections in contacts
- On-device contact matching
- Works via Catalyst on Mac
Read full descriptionHide full description
Time isn’t just 6:31. It’s 631 - a prime! A lucky prime... It’s the combination to the bike lock you had as a kid. It might be the last digits of the cell phone of someone you love. This is a clock for people who notice things like that. Every minute, it: • Computes mathematical properties of the current time • Surfaces number theory facts (prime, factorization, powers, sequences, curiosities) • Scrambles them onto glowing 16-segment LED displays, like your old Speak 'n Spell • Optionally finds personal number connections in your contacts — entirely on device Works great as a Mac app via Catalyst. Contact matching happens entirely on device. No personal data is ever transmitted. Usage analytics (anonymous) are collected to improve the app. If you’ve ever factored timestamps in your head, smiled at 5:12 = 2⁹, or paused at 17:29… This is the clock for you. Make every minute momentous.
Screenshots
Verdict
The clearest difference is update cadence: Momentous Clock at every 6 days against Primality's every 2 months. Primality's advantage is ratings volume (24 vs 2) and iOS requirement (13.2 vs 15.1). On price, rating, ads and in-app purchases there is nothing between them.
Scored on Price · Rating · Positive reviews · Number of ratings · Update frequency · Ads · In-app purchases · Monetization · Best chart rank · Devices · Requires iOS
Both are free to download. Neither carries in-app purchases, so what you see is what you pay.
On the App Store both sit at effectively the same score — 4.9 for Primality against 5.0 for Momentous Clock. That said, the two scores are not equally well evidenced: Primality has 24 ratings behind it against 2, so its average is the more settled of the two.
Primality ships an update every 2 months, Momentous Clock every 6 days. The most recent releases landed on September 27, 2026 and October 3, 2026 respectively.
| Parameter | Primality | Momentous Clock |
|---|---|---|
| Price | Free | Free |
| Rating | 4.9 (24 ratings) | 5.0 (2 ratings) — better |
| Positive reviews | 100.0% of reviews | — |
| Number of ratings | 24 — better | 2 |
| Update frequency | Every 2 months | Every 6 days — better |
| Ads | No | No |
| In-app purchases | No | No |
| Monetization | Free | Free |
| Devices | iPhone, iPod | iPhone, iPad, iPod — better |
| Requires iOS | 13.2 — better | 15.1 |
| Further details — not scored | ||
| Size | 1 MB | 24 MB |
| Age rating | 4+ | 4+ |
| Developer | Bruce Schechter | Tutukain Software, LLC |
Customer experience
Primality
Momentous Clock
In-app purchases
Primality
No in-app purchases
Momentous Clock
No in-app purchases
Questions
Is Primality free?
Is Momentous Clock free?
Which has better reviews, Primality or Momentous Clock?
Do Primality or Momentous Clock have ads?
Which is updated more often, Primality or Momentous Clock?
Other comparisons
