<p>Overall, you have to start with a "1" (unless you're doing alt-coins). Then the first letter is the only one that can be more tricky to generate (<a href="https://bitcoin.stackexchange.com/q/3854/323">some letters from the end of the Base58 alphabet are harder</a>). Also, generating an address with a lot of leading 1s is a lot harder than any other characters due to <a href="https://en.bitcoin.it/wiki/Base58Check_encoding" rel="nofollow noreferrer">how addresses are constructed</a> (leading 1s mean that you have a whole leading byte of 0x00 at the start of the address, or about 1 in 255 change in comparison to 1 in 58 chance for any other letter). After the leading 1s and the first letter, everything else is the same 1 in 58 chance of being any letter no matter what it is.</p>

<p>So all in all, you can generate any combination of letters and numbers in a Bitcoin address as long as it starts with "1", but some combinations are harder to generate. The same can't be said for other altcoins with a specific netbyte, since some starting patterns may be outside of their name space.</p>

CC BY-SA 3.0
2013-10-30T04:06:57.223Z
from the link regarding the base58 address space they do not mention the difficulty of getting an address that begins with 10, or does the zero fall after 9 and before A?
Mark S.
CC BY-SA 3.0
2013-10-30T04:13:21.283Z
nevermind I see 0 is not part of the base58 implementation to prevent confusion with the capital O.
Mark S.
CC BY-SA 3.0
2014-04-06T19:33:51.993Z
In addition to the above answer, 0 (zero), O (uppercase letter o), l (lowercase letter L) and I (uppercase letter i) are not allowed in Bitcoin addresses because they can be ambiguous.
CPomerantz
CC BY-SA 3.0
2013-10-30T03:57:01.423Z
2013-10-30T03:57:01.423Z
2017-04-13T12:47:34.187Z
ThePiachu
<p>I have noticed that many bitcoin addresses begin with numbers or uppercase characters. I realize that all addresses begin with the number one but can I generate an address with the second character being lowercase?  Is it significantly harder to generate an address with multiple lowercase letters at the beginning? Are there any other limitations in regards to generating vanity addresses?  </p>

<vanity-address><vanitygen>
Are there any limitations to vanity addresses?
Mark S.
# Are there any limitations to vanity addresses?

(Asked by: username_0 on 2013-10-30)

I have noticed that many bitcoin addresses begin with numbers or uppercase characters. I realize that all addresses begin with the number one but can I generate an address with the second character being lowercase? Is it significantly harder to generate an address with multiple lowercase letters at the beginning? Are there any other limitations in regards to generating vanity addresses?

**Tags:** vanity-address, vanitygen


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## 1 answers

### Answer by username_1 on 2013-10-30. Score: 2 | Accepted answer

Overall, you have to start with a "1" (unless you're doing alt-coins). Then the first letter is the only one that can be more tricky to generate ([some letters from the end of the Base58 alphabet are harder](https://bitcoin.stackexchange.com/q/3854/323)). Also, generating an address with a lot of leading 1s is a lot harder than any other characters due to [how addresses are constructed](https://en.bitcoin.it/wiki/Base58Check_encoding) (leading 1s mean that you have a whole leading byte of 0x00 at the start of the address, or about 1 in 255 change in comparison to 1 in 58 chance for any other letter). After the leading 1s and the first letter, everything else is the same 1 in 58 chance of being any letter no matter what it is.

So all in all, you can generate any combination of letters and numbers in a Bitcoin address as long as it starts with "1", but some combinations are harder to generate. The same can't be said for other altcoins with a specific netbyte, since some starting patterns may be outside of their name space.

> **Comments:**
> **username_0**: from the link regarding the base58 address space they do not mention the difficulty of getting an address that begins with 10, or does the zero fall after 9 and before A?  
> **username_0**: nevermind I see 0 is not part of the base58 implementation to prevent confusion with the capital O.  
> **username_2**: In addition to the above answer, 0 (zero), O (uppercase letter o), l (lowercase letter L) and I (uppercase letter i) are not allowed in Bitcoin addresses because they can be ambiguous.  

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