Naoki Chigira Masaaki Harada Masaaki Kitazume Extremal self-dual codes of length 64 through neighbors and covering radii. 93-101 2007 42 Des. Codes Cryptography 1 http://dx.doi.org/10.1007/s10623-006-9018-5 db/journals/dcc/dcc42.html#ChigiraHK07