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A128902
Number of degree n polynomials over GF(2) (with nonzero constant term) at Hamming distance 2 from some irreducible polynomial.
The coefficient vectors of the three degree 4 irreducible polynomials are 10011, 11111 and 11001. There is only one polynomial whose Hamming distance is two (or more) from all of them, namely 10101. Thus a(4) = |{10101}| = 1.