A056275 - OEIS

%I #10 Jan 18 2022 14:40:55

%S 1,1,4,13,50,181,714,2780,11046,43895,175274,699875,2798250,11188191,

%T 44747380,178970560,715860650,2863365834,11453377194,45813202675,

%U 183252461532,733008625151,2932033104554,11728127521060,46912504507000,187649998452735,750599971438464

%N Number of primitive (aperiodic) word structures of length n using a 4-ary alphabet.

%C Permuting the alphabet will not change a word structure. Thus aabc and bbca have the same structure.

%D M. R. Nester (1999). Mathematical investigations of some plant interaction designs. PhD Thesis. University of Queensland, Brisbane, Australia. [See A056391 for pdf file of Chap. 2]

%F a(n) = Sum_{d|n} mu(d)*A007581(n/d-1).

%Y Cf. A008683, A054719.

%K nonn

%O 1,3

%A _Marks R. Nester_