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A215090 a(n) = Sum_{i=0..m} d(i)*3^i, where Sum_{i=0..m} d(i)*4^i is the base-4 representation of n.

%I A215090 #24 Jan 03 2021 14:36:44
%S A215090 0,1,2,3,3,4,5,6,6,7,8,9,9,10,11,12,9,10,11,12,12,13,14,15,15,16,17,
%T A215090 18,18,19,20,21,18,19,20,21,21,22,23,24,24,25,26,27,27,28,29,30,27,28,
%U A215090 29,30,30,31,32,33,33,34,35,36,36,37,38,39,27,28,29,30,30,31,32
%N A215090 a(n) = Sum_{i=0..m} d(i)*3^i, where Sum_{i=0..m} d(i)*4^i is the base-4 representation of n.
%H A215090 Seiichi Manyama, <a href="/A215090/b215090.txt">Table of n, a(n) for n = 0..10000</a> (terms 0..1000 from Clark Kimberling)
%F A215090 a(n) = 3*a(n/4) if n == 0 (mod 4); otherwise a(n) = a(n-1)+1.
%t A215090 t = Table[FromDigits[RealDigits[n, 4], 3], {n, 0, 100}]
%o A215090 (PARI) a(n) = fromdigits(digits(n, 4), 3); \\ _Michel Marcus_, May 02 2018
%o A215090 (Julia)
%o A215090 function a(n)
%o A215090     m, r, b = n, 0, 1
%o A215090     while m > 0
%o A215090         m, q = divrem(m, 4)
%o A215090         r += b * q
%o A215090         b *= 3
%o A215090     end
%o A215090 r end; [a(n) for n in 0:70] |> println # _Peter Luschny_, Jan 03 2021
%Y A215090 Cf. A023717.
%K A215090 nonn,base,easy
%O A215090 0,3
%A A215090 _Clark Kimberling_, Aug 03 2012