# 空の青さを知る vs THE 13th Digit

The clearest difference is in-app purchases: 空の青さを知る at none against THE 13th Digit's 1. THE 13th Digit's advantage is update cadence (every 3 days vs monthly). On price, ads, device support and iOS requirement there is nothing between them.

Both are free to download. THE 13th Digit sells 1 one-off in-app purchase. 空の青さを知る asks for nothing beyond the download.

空の青さを知る ships an update monthly, THE 13th Digit every 3 days. The most recent releases landed on October 3, 2026 and September 30, 2026 respectively.

## The numbers

| Metric | 空の青さを知る | THE 13th Digit |
| --- | --- | --- |
| Price | Free | Free |
| In-app purchases | **No** | Yes |
| Ads | No | No |
| Update frequency | Monthly | **Every 3 days** |
| Size | 86 MB | 190 MB |
| Requires iOS | 15.5 | **14.0** |
| Devices | iPhone, iPod | iPhone, iPod |
| Age rating | 9+ | 12+ |
| Developer | [chiaki matsuda](https://appshunter.io/developer/1602664460) | [UESHO K.K.](https://appshunter.io/developer/6776764835) |

## What reviewers say

### 空の青さを知る

[App page](https://appshunter.io/ios/app/id1602664458)

**Features:** macOS Compatibility

**In-app purchases:** none


### THE 13th Digit

[App page](https://appshunter.io/ios/app/the-13th-digit/id6787610293)

**Features:** macOS Compatibility

**In-app purchases (1)**

| Purchase | Price | Billing |
| --- | --- | --- |
| 2周目〈NG+〉解放 | $1.99 | one-time |


## Frequently asked questions

### Is 空の青さを知る free?

空の青さを知る is free to download, with no in-app purchases.

### Is THE 13th Digit free?

THE 13th Digit is free to download, with in-app purchases available.

### Do 空の青さを知る or THE 13th Digit have ads?

Neither 空の青さを知る nor THE 13th Digit shows ads.

### Which is updated more often, 空の青さを知る or THE 13th Digit?

空の青さを知る ships an update monthly, and THE 13th Digit every 3 days. Most recently, 空の青さを知る was updated on October 3, 2026 and THE 13th Digit on September 30, 2026.

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