Information on mass chains and nuclides available on this website:

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¹⁹C may have been observed in the 3 GeV proton bombardment of a ¹⁹⁷Au target: if so it is particle stable (RA70). Its mass excess must then be < 37.9 MeV (¹⁸C + n). See also (ZE60A, BU71E).