This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A291770 #20 May 15 2021 06:18:08
%S A291770 0,0,1,0,0,1,0,0,3,2,2,1,0,0,1,0,0,3,2,2,1,0,0,1,0,0,7,6,6,5,4,4,5,4,
%T A291770 4,3,2,2,1,0,0,1,0,0,3,2,2,1,0,0,1,0,0,7,6,6,5,4,4,5,4,4,3,2,2,1,0,0,
%U A291770 1,0,0,3,2,2,1,0,0,1,0,0,15,14,14,13,12,12,13,12,12,11,10,10,9,8,8,9,8,8,11,10,10,9,8,8,9,8,8,7,6,6
%N A291770 A binary encoding of the zeros in ternary representation of n.
%C A291770 The ones in the binary representation of a(n) correspond to the nonleading zeros in the ternary representation of n. For example: ternary(33) = 1020 and binary(a(33)) = 101 (a(33) = 5).
%H A291770 Antti Karttunen, <a href="/A291770/b291770.txt">Table of n, a(n) for n = 1..59049</a>
%F A291770 For all n >= 0, a(A000244(n)) = A000225(n), that is, a(3^n) = (2^n) - 1. [The records in the sequence].
%F A291770 For all n >= 1, A000120(a(n)) = A077267(n).
%F A291770 For all n >= 1, A278222(a(n)) = A291771(n).
%e A291770 n a(n) ternary(n) binary(a(n))
%e A291770 A007089(n) A007088(a(n))
%e A291770 -- ---- ---------- ------------
%e A291770 1 0 1 0
%e A291770 2 0 2 0
%e A291770 3 1 10 1
%e A291770 4 0 11 0
%e A291770 5 0 12 0
%e A291770 6 1 20 1
%e A291770 7 0 21 0
%e A291770 8 0 22 0
%e A291770 9 3 100 11
%e A291770 10 2 101 10
%e A291770 11 2 102 10
%e A291770 12 1 110 1
%e A291770 13 0 111 0
%e A291770 14 0 112 0
%e A291770 15 1 120 1
%e A291770 16 0 121 0
%e A291770 17 0 122 0
%e A291770 18 3 200 11
%e A291770 19 2 201 10
%e A291770 20 2 202 10
%e A291770 21 1 210 1
%e A291770 22 0 211 0
%e A291770 23 0 212 0
%e A291770 24 1 220 1
%e A291770 25 0 221 0
%e A291770 26 0 222 0
%e A291770 27 7 1000 111
%e A291770 28 6 1001 110
%e A291770 29 6 1002 110
%e A291770 30 5 1010 101
%t A291770 Table[FromDigits[IntegerDigits[n, 3] /. k_ /; k < 3 :> If[k == 0, 1, 0], 2], {n, 110}] (* _Michael De Vlieger_, Sep 11 2017 *)
%o A291770 (Scheme) (define (A291770 n) (if (zero? n) n (let loop ((n n) (b 1) (s 0)) (if (< n 3) s (let ((d (modulo n 3))) (if (zero? d) (loop (/ n 3) (+ b b) (+ s b)) (loop (/ (- n d) 3) (+ b b) s)))))))
%o A291770 (Python)
%o A291770 from sympy.ntheory.factor_ import digits
%o A291770 def a(n):
%o A291770 k=digits(n, 3)[1:]
%o A291770 return int("".join('1' if i==0 else '0' for i in k), 2)
%o A291770 print([a(n) for n in range(1, 111)]) # _Indranil Ghosh_, Sep 21 2017
%Y A291770 Cf. A007088, A007089, A077267, A289813, A289814, A291771.
%K A291770 nonn,base
%O A291770 1,9
%A A291770 _Antti Karttunen_, Sep 11 2017