Abstract-Somenew examples of binary Bose-ChaudhuriHoquengkn (BCH) codes of length 255 are found for which tbe minimum distance and designed dishace agree.For a cyclic code of length n with generating polynomial g(x), the designed distance S is defined as follows: 6-1 is the maximum length of a string of consecutive powers of a which are zeros of g (x), where a is a primitive nth root of unity. It is known (see e.g. [l, p. 2011) that S is a lower bound on the true minimum distance d. For most Bose-Chaudhuri-Hocquenghen (BCH) codes of primitive length (n x2"--1) we have d= 6, the first example of nonequality being n = 127, 8 -29, d=31 ([ 1, p. 2671).Kasami [2] proved that when m # 8, 12 and m > 6, there exist binary BCH codes with d >I% Thus n = 255 is the first length for which it is not known when d = S or d >I% The aim of this correspondence is to prove that d= 6 for 6 = 37, 39, 45, 87 removing some asterisks from [ 1, p. 2671. Still unsettled values are S =43, 53, 59, 61, 91. We shall make use of the following theorem.Theorem ([3, p. 2781): Let n, and n2 be relatively prime and let a be a factor of ni. If a BCH code of length n2 and designed distance d has minimum distance exactly d, then the BCH code of length nln2 and designed distance ad has minimum distance exactly ad.In [4, table I] we find d= 6 for 9
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