That's the Snapper S/N, I suspect that the 1st digit, "1", is 1981, and the 2ed is the month, "4" is Apr.
The engine S/N will be on a metal plate on the engine. With that vintage Onan, the letter is the month, the next 2 digits is the year.
If it is still there, it's on the top of the blower sheet metal under the throttle linkage.
Sorry about the mix up. The model number on metal tag to engine reads: ?48M-GA 018/3421A. The serial number reads: F793471706.