The 1936 Lincoln series had quite a few obverse dies that were created from a working hub that had a broken R in LIBERTY. Your coin was struck from one of those "broken R" dies.
Well, if an error is something less than perfection, then yes, it is an error. The questions then are: 1) how rare is it; and 2) is it an error people are willing to pay a premium for? It appears that cents exhibiting an R like yours are common and there are probably enough are around to meet demand. Therefore, any premium would be minimal (if any). However, I do not think this is the kind of error collectors just have to have as part of their Lincoln collection. It is probably undesirable, thus would not be sought after by most, especially those looking for a coin with full details.
i sold this one for a premium.the only one i ever found in us cents,i regret it now because i have found a few more lately....