# f(x) vs Constant Challenge

The clearest difference is in-app purchases: f(x) at none against Constant Challenge's 3. f(x) also leads on iOS requirement (15.0 vs 26.0). Constant Challenge's advantage is update cadence (every 2 days vs monthly). On price, ads and device support there is nothing between them.

Both are free to download. Constant Challenge sells 3 one-off in-app purchases. f(x) asks for nothing beyond the download.

f(x) ships an update monthly, Constant Challenge every 2 days. The most recent releases landed on September 25, 2026 and September 28, 2026 respectively.

## The numbers

| Metric | f(x) | Constant Challenge |
| --- | --- | --- |
| Price | Free | Free |
| In-app purchases | **No** | Yes |
| Ads | No | No |
| Update frequency | Monthly | **Every 2 days** |
| Size | 77 MB | 16 MB |
| Requires iOS | **15.0** | 26.0 |
| Devices | **iPhone, iPad, iPod** | iPhone, iPad |
| Age rating | 12+ | 4+ |
| Developer | [Ryo Matsumoto](https://appshunter.io/developer/1725054568) | [Kaname Inoue](https://appshunter.io/developer/1888387338) |

## What reviewers say

### f(x)

[App page](https://appshunter.io/ios/app/fx/id6475749250)

**Features:** macOS Compatibility, Vision Pro support

**In-app purchases:** none


### Constant Challenge

[App page](https://appshunter.io/ios/app/constant-challenge/id6761248442)

**Features:** macOS Compatibility

**In-app purchases (3)**

| Purchase | Price | Billing |
| --- | --- | --- |
| Unlock the Square Root of 2 (√2) | $0.99 | one-time |
| Unlock the Golden Ratio (φ) | $0.99 | one-time |
| Unlock the Euler–Mascheroni (γ) | $0.99 | one-time |


## Frequently asked questions

### Is f(x) free?

f(x) is free to download, with no in-app purchases.

### Is Constant Challenge free?

Constant Challenge is free to download, with in-app purchases available.

### Do f(x) or Constant Challenge have ads?

Neither f(x) nor Constant Challenge shows ads.

### Which is updated more often, f(x) or Constant Challenge?

f(x) ships an update monthly, and Constant Challenge every 2 days. Most recently, f(x) was updated on September 25, 2026 and Constant Challenge on September 28, 2026.

---

*Compared by [AppsHunter](https://appshunter.io/) from daily US App Store data. Review summaries are generated from verbatim App Store reviews.*