user106912: I've obtained a list of all current Bitcoin addresses with balances from Blockchair, which is downloadable from their data repository located here.  I have downloaded the Bitcoin / Addresses TSV database dump.
The list consists of:

~23m P2PKH (1xxx) addresses
~5.8m P2SH (3xxx) addresses
~1.3m Bech32 (bc1xxx) addresses

However, there are also ~400k addresses that have prefixes that I don't recognise, including:

d-xxx (example: d-b697921d996831d1a26ca8d8e92571c1)
m-xxx (example: m-942943e227462513f33c4f32ec6f1e56)
s-xxx (example: s-2ad548f2459c0ed6123400e5d61a479e)

Are these valid Bitcoin addresses?
If they are, how do I view information about them?
If they are not, any idea why they appear in the dump of current Bitcoin addresses from Blockchair?

user38618: Those are invalid addresses that don't belong to any cryptocurrency. You should file a bug report at https://github.com/Blockchair/Blockchair.Support/issues since those might even be their database secrets.
Those are of 16 bytes. My initial guess about their format would be SHA-1, but Bitcoin does not use SHA-1. Probably it's related to their database.
For example on this page https://blockchair.com/dogecoin/address/942943e227462513f33c4f32ec6f1e56 it seems Blockchair thinks 942943e227462513f33c4f32ec6f1e56 is a valid Doge address. It's not.
To prevent this from happening again in the future, they could implement input sanitization before INSERT statements

user106912: Having investigated this following @MCCCS answer, the following is information about the addresses provided by Blockhair support:

In fact, there are no addresses on the Bitcoin blockchain. There are
only scripts, some of them are standard and can be converted to a
Bitcoin address, some of them can’t — like nulldata (OP_RETURN)
outputs, nonstandard, and bare multisig. We use the d- prefix for
nulldata, m- for bare multisig, and s- for everything else.
This is briefly mentioned in this API documentation section:
https://blockchair.com/api/docs#link_300

Therefore, these addresses (for want of a better word) are valid transactions on the Bitcoin blockchain.
The prefixes used are:

d- nulldata
m- bare multisig
s- everything else

In conclusion, the data is valid but the outputs are not addresses in the normal sense of the word.
A link to the issue I raised on the Blockchair GitHub is here.

106912: <p>I've obtained a list of all current Bitcoin addresses with balances from Blockchair, which is downloadable from their data repository located <a href="https://blockchair.com/dumps" rel="nofollow noreferrer">here</a>.  I have downloaded the <code>Bitcoin / Addresses</code> TSV database dump.</p>
<p>The list consists of:</p>
<ul>
<li>~23m P2PKH (<code>1xxx</code>) addresses</li>
<li>~5.8m P2SH (<code>3xxx</code>) addresses</li>
<li>~1.3m Bech32 (<code>bc1xxx</code>) addresses</li>
</ul>
<p>However, there are also ~400k addresses that have prefixes that I don't recognise, including:</p>
<ul>
<li>d-xxx (example: <code>d-b697921d996831d1a26ca8d8e92571c1</code>)</li>
<li>m-xxx (example: <code>m-942943e227462513f33c4f32ec6f1e56</code>)</li>
<li>s-xxx (example: <code>s-2ad548f2459c0ed6123400e5d61a479e</code>)</li>
</ul>
<p><strong>Are these valid Bitcoin addresses?</strong></p>
<p>If they are, how do I view information about them?</p>
<p>If they are not, any idea why they appear in the dump of current Bitcoin addresses from Blockchair?</p>
 38618: <p>Those are invalid addresses that don't belong to any cryptocurrency. You should file a bug report at <a href="https://github.com/Blockchair/Blockchair.Support/issues" rel="nofollow noreferrer">https://github.com/Blockchair/Blockchair.Support/issues</a> since those might even be their database secrets.</p>
<p>Those are of 16 bytes. My initial guess about their format would be SHA-1, but Bitcoin does not use SHA-1. Probably it's related to their database.</p>
<p>For example on this page <a href="https://blockchair.com/dogecoin/address/942943e227462513f33c4f32ec6f1e56" rel="nofollow noreferrer">https://blockchair.com/dogecoin/address/942943e227462513f33c4f32ec6f1e56</a> it seems Blockchair thinks <code>942943e227462513f33c4f32ec6f1e56</code> is a valid Doge address. It's not.</p>
<p>To prevent this from happening again in the future, they could implement input sanitization before INSERT statements</p>
 106912: <p>Having investigated this following @MCCCS <a href="https://bitcoin.stackexchange.com/a/96780/106912">answer</a>, the following is information about the addresses provided by Blockhair support:</p>
<blockquote>
<p>In fact, there are no addresses on the Bitcoin blockchain. There are
only scripts, some of them are standard and can be converted to a
Bitcoin address, some of them can’t — like nulldata (OP_RETURN)
outputs, nonstandard, and bare multisig. We use the d- prefix for
nulldata, m- for bare multisig, and s- for everything else.</p>
<p>This is briefly mentioned in this API documentation section:
<a href="https://blockchair.com/api/docs#link_300" rel="noreferrer">https://blockchair.com/api/docs#link_300</a></p>
</blockquote>
<p>Therefore, these <em>addresses</em> (for want of a better word) are valid transactions on the Bitcoin blockchain.</p>
<p>The prefixes used are:</p>
<ul>
<li><code>d-</code> nulldata</li>
<li><code>m-</code> bare multisig</li>
<li><code>s-</code> everything else</li>
</ul>
<p>In conclusion, the <strong>data is valid</strong> but the outputs are not addresses in the normal sense of the word.</p>
<p>A link to the issue I raised on the Blockchair GitHub is <a href="https://github.com/Blockchair/Blockchair.Support/issues/273" rel="noreferrer">here</a>.</p>
