a(n) = length of (n+1)st run, with initial terms 1, 2.

Terms

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