%I
%S 0,0,1,1,1,0,0,0,0,1,1,1,1,0,0,0,0,0,1,1,1,0,0,0,0,0,1,1,1,0,0,0,0,0,
%T 1,1,1,1,0,0,0,0,1,1,1,1,0,0,0,0,0,1,1,1,0,0,0,0,0,1,1,1,0,0,0,0,0,1,
%U 1,1,1,0,0,0,0,0,1,1,1,0,0,0,0,0,1,1,1,0,0,0,0,0,1,1,1,0,0,0,0,0,1,1,1,1,0,0,0,0,0,1,1
%N Second most significant bit of the tribonacci number A000073(n).
%C It is conjectured that after the first two 0's, the number of consecutive 0's is only 4 or 5, and the number of consecutive 1's is only 3 or 4 (tested up to n=10^4). The sequence looks quasiperiodic (or with a very long true period if any).
%H Chai Wah Wu, <a href="/A271591/b271591.txt">Table of n, a(n) for n = 4..10000</a>
%F a(n) = floor(A000073(n)/(2^(ceiling(log_2(A000073(n) + 1))  2)))  2.
%F a(n) = A079944(A000073(n)2).  _Michel Marcus_, Apr 22 2016
%e (Second MSB in parenthesis)
%e n A000073(n) A000073(n)
%e decimal binary
%e 4 2 > 1(0)
%e 5 4 > 1(0)0
%e 6 7 > 1(1)1
%e 7 13 > 1(1)01
%e 8 24 > 1(1)000
%e 9 44 > 1(0)1100
%e 10 81 > 1(0)10001
%e 11 149 > 1(0)010101
%t a = LinearRecurrence[{1, 1, 1}, {0, 0, 1}, 120];(* to generate A000073 *)
%t Table[IntegerDigits[a, 2][[i]][[2]], {i, 5, Length[a]}]
%o (Python)
%o A271591_list, a, b, c = [], 0, 1 ,1
%o for n in range(4,10001):
%o a, b, c = b, c, a+b+c
%o A271591_list.append(int(bin(c)[3])) # _Chai Wah Wu_, Feb 07 2018
%Y Cf. A000073 (tribonacci numbers), A079944 (2nd msb), A272170.
%K nonn,base
%O 4,1
%A _Andres Cicuttin_, Apr 10 2016
