Least k>1 such that first n terms of A006928 repeat beginning at k-th term.

Terms

a(0) =3a(1) =4a(2) =4a(3) =13a(4) =13a(5) =19a(6) =19a(7) =19a(8) =19a(9) =28a(10) =28a(11) =28a(12) =28a(13) =28a(14) =28a(15) =100a(16) =100a(17) =405a(18) =405a(19) =405a(20) =405a(21) =405a(22) =405a(23) =405a(24) =608a(25) =608a(26) =608a(27) =608a(28) =608a(29) =608