Yes:

    817023023960376946633975507110154649249407598806798730414849884461776172171921668594148071323527016137506405823108520062504849249423700259406905313281403901410082762097159560221463048924336192384026777502177262731045200322200149773127502888545234973139480887644585192600631058962876114156934248895171959246969597637127280010272143593885240940877456234662196130491400738438731832514335353824697930453078426722191105157568392826870043655708008545411143367763836566011740499383456592129662585004880376777597714978023542434421914201119537685489173509942329090631662014650033142642110914360849421856179611226450806562235534802516081595259914768497444702718749402330070488028751073730349460752771915484847399385631524708487646079936572410398967582895983187640798072309362094727654167628620105981459021548290415800096769214437425690934372015628796027498219902441288189398386359846661623243493534897411417685435424010451956954083531228374002591372549525280610594684910812811287436481207089763125424247793044043309737269468709710679872269272855389945385386467765509880648929743498214329578288874987193768439353382305260108425688024147656806932474058888992099083804597481699305852902662863062054067183925164590726103552998367994727700722491707 `mod` 231
    0

Wait a minute, I get a different n value by downloading that key and running gpg --list-keys --with-key-data on it.

You have one ending in 131307671292149646652772992033083 and I have one ending in 726103552998367994727700722491707 that is not divisible by 231.

The key as seen by Phuctor had three sub-keys, one of which was an RSA key which turned out to be factorable.

Sorry, I was looking at the other one. But something is still very, very odd. (1) Two of the subkeys agree with one another for hundreds of digits and then disagree. (2) I did gpg --recv-key 51221121 and I got a key back from the keyserver with fingerprint 7EAA C969 3E7D 2205 46BE 576C BDA0 6085 493B ACE4 (only, no other keys) -- which doesn't match the key ID that it should, and is seemingly missing the vulnerable subkey entirely.

Can you post the ASCII-armored key that you have? I am getting a radically different key from the keyservers, and I wonder if there could be some kind of keyserver attack or misbehavior involved here too.

Well, it lists the key and says the first factor is 231. If you have a big enough calculator, this is trivial to verify.

Author of 'phuctor' speaking.

I can only confirm that we have a key, downloaded from an SKS dump, said key purporting to belong to one Mr. Anvin, containing one sub-key being an RSA public key which turned out to be factorable with trivial effort.

Anything else is mere conjecture.

You can confirm this independently with the key itself and the published prime.

I too can post a public key I have the private key for and a factor? Or intentionally create a weak key?

Yes you can, we just need to find hpa's n value and see whether it is divisible by 231. If it is, the claim is correct.

I found the n value for my own PGP public key before and I can find hpa's too, I just have to remember the right arguments to gpg.

It's: gpg --list-key --with-key-data <id>

    $ gpg --export -a $$KEYID$$ >keyfile.asc   
    $ gpg --list-packets --debug=0x02 keyfile.asc

...but I don't know if the pkey[] values are directly usable, or have some substructure.

you can trivially verify a key was broken if it was, duh, broken