That's a rare one indeed, in the Lightweight range but not a Lightweight. I have 244064, a convertible in about 98% condition and a 4 digit valuation.
The bulk of the 2xxxxx SN range was reserved for the 1950's Lightweight Single Sixes with aluminum alloy cylinder frames. Ruger seemed to have started to reuse that range in the early 1960s with these guns, then changed their mind and switched to the 4xxxxx range (because the 3xxxxx range was reserved for the 6.5" RSSM and RSSMX). In later years, there were some other barrel lengths in the upper 3xxxxx range but only that brief burst of non-Lightweights in the 2xxxxx range. After 4xxxxx was exhausted, they jumped to 8xxxxx because the 5xxxxx range was reserved for adjustable sight Super Single Sixes and they probably thought those would just keep going into 6xxxxx and 7xxxxx but GCA68 dashed those plans by requiring every serial number from a manufacturer to ID one and only one gun, so Ruger complied with the prefixed numbers starting in 1969.