It's The Head, Silly!

((( That's a new one, at least for me. What does the 'N' mean? )))

As Dave points out, "N-4" is a shorthand way of stating that the die marriage for this particular coin is "Newcomb Four". "Die marriage" refers to the combination of a specific obverse die with a specific reverse die, and each such unique combination of dies is assigned a "Newcomb" attribution.

Suppose that in 1837, two obverse dies, "O1" and "O2" were used, along with two reverse dies, "R1" and "R2" (typically for early coins, ten or so obverse and reverse dies might be used per year). Mathematically, this would allow for four possible die marriages, O1+R1, O1+R2, O2+R1, and O2+R2. Now, in reality, it's quite possible that some die marriages never occurred. For example, suppose O1 broke shortly after being put into use R1, and never had an opportunity to be paired with R2. In that case, the date would only have three die-marriages (O1+R1, O2+R1, O2+R2). In this case, we would have attributed Newcomb varieties, N1 = O1+R1, N2 = O2+R1 and N3 = O2+R2.

Kinda looks like chemistry, doesn't it?

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Mila_Cent, that refers the the Newcomb variety, after H.R. Newcomb, who first described the varying die states and varieties of Large Cents. Newcomb numbers are to Large Cents what VAM's are to Morgans.

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Actually Newcomb wasn't the first. His work built on the work of his mentor Andrews (first name escapes me at the moment) Andrews published his work on the die varieties of large cents from 1816 to 1857 in 1882 with a second edition published in 1883. Newcomb expanded the late date varieties considerably but most of the Necomb book on the middle dates is simply the Andrews book with the A numbers changed to N numbers. The few additions are tacked onto the end of each year.
Even though Newcomb book has been superceded it still has a strong influence on the collecting community. When the update to the middle dates was planned it was intended to update the emission sequence and to renumber the series based on how they were issued. With the late dates a great many of the Newcomb varieties have been delisted and renumbering here would have also made sense. But in the end the old Newcomb numbers have prevaled and for one of the first times the varieties numbers for a series do NOT reflect the name of the author of the standard reference for the series.