I want to sign up to this website that has an English version, but
unfortunately, the captcha for it is Japanese. I can't read Japanese and no
online translator seems to be able to make sense of the 2nd line. Here it is:

> 表示されている数式を計算して、半角数字で答えを入力してください: 必須（半角数字）

> ろクタスナナは

[![enter image description
here](https://i.stack.imgur.com/zgx09.png)](https://i.stack.imgur.com/zgx09.png)

Why is this an effective captcha?

I'd also like to know the meaning, the translation, and why no translator
seems to be able to translate that last word.

Thanks.
CC BY-SA 4.0
2021-06-28T22:54:47.367
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2021-06-28T23:11:32.923
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question
meaning translation katakana
Why is this an effective captcha?
It shows ”ろく たす なな“. To obfuscate sentence, It use combination of HIRAGANA and
KATAKANA.

6+7
CC BY-SA 4.0
2021-06-28T23:05:38.370
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2021-06-28T23:05:38.370
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answer