JNat's answer is correct. Just to add a bit of info:

The variants of "Shibuimaru" that he tries are:

渋井丸
渋伊丸

Note the differences in the middle character.

The variants of "Takuo" that he tries are:

拓男
拓夫
拓雄
卓男

I think we encounter another minor plot hole here (at least as shown in the anime) - Light stops writing after iterating over all 8 combinations of those names (the first of which, 渋井丸 拓男, turns out to be correct), when there are actually at least 2 more spellings of "Takuo" (卓夫 and 卓雄) that should've been possible.

JNat's answer is correct. Just to add a bit of info:

The variants of "Shibuimaru" that he tries are:

渋井丸
渋伊丸

Note the differences in the middle character.

The variants of "Takuo" that he tries are:

拓男
拓夫
拓雄
卓男

I think we encounter another minor plot hole here (at least as shown in the anime) - Light stops writing after iterating over all 8 combinations of those names (the first of which, 渋井丸 拓男, turns out to be correct), when there are actually at least 2 more spellings of "Takuo" (卓夫 and 卓雄) that should've been possible.

JNat's answer is correct. Just to add a bit of info:

The variants of "Shibuimaru" that he tries are:

渋井丸
渋伊丸

Note the differences in the middle character.

The variants of "Takuo" that he tries are:

拓男
拓夫
拓雄
卓男

I think we encounter another minor plot hole here (at least as shown in the anime) - Light stops writing after iterating over all 8 combinations of those names (the first of which, 渋井丸 拓男, turns out to be correct), when there are actually at least 2 more spellings of "Takuo" (卓夫 and 卓雄) that should've been possible.

JNat's answer is correct. Just to add a bit of info:

The variants of "Shibuimaru" that he tries are:

渋井丸
渋伊丸

Note the differences in the middle character.

The variants of "Takuo" that he tries are:

拓男
拓夫
拓雄
卓男

I think we encounter another minor plot hole here (at least as shown in the anime) - Light stops writing after iterating over all 8 combinations of those names (the first of which, 渋井丸 拓男, turns out to be correct), when there are actually at least 2 more spellings of "Takuo" (卓夫 and 卓雄) that should've been possible.