$ n = 5k + 2 $
$ B = a^6 + a^4 + 4a^2 + 4 \\ = a^4(a^2 + 1) + 4(a^2 + 1) \\ = (a^2 + 1)(a^4 + 4) \\ = [(5k + 2)^2 + 1][(5k + 2)^4 + 4] \\ = (25k^2 + 20k + 4 + 1)(625k^4 + 1000k^3 + 600k^2 + 160k + 16 + 4) \\ = (25k^2 + 20k + 5)(625k^4 + 1000k^3 + 600k^2 + 160k^2 + 20) \\ = 5(5k^2 + 4k + 1) ...