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The binary representation of a(n) is the concatenation of n and the binary complement of n, A035327(n).
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%I #19 May 05 2021 13:40:27

%S 2,9,12,35,42,49,56,135,150,165,180,195,210,225,240,527,558,589,620,

%T 651,682,713,744,775,806,837,868,899,930,961,992,2079,2142,2205,2268,

%U 2331,2394,2457,2520,2583,2646,2709,2772,2835,2898,2961,3024,3087,3150,3213

%N The binary representation of a(n) is the concatenation of n and the binary complement of n, A035327(n).

%H Michael De Vlieger, <a href="/A253608/b253608.txt">Table of n, a(n) for n = 1..10000</a>

%F a(n) = (n+1) * (2^BL(n) - 1), where BL(n) is the binary length of n.

%p a:= n-> (n+1)*(2^(ilog2(n)+1)-1):

%p seq(a(n), n=1..50); # _Alois P. Heinz_, Jan 08 2015

%t Array[(# + 1) (2^(Floor@ Log2[#] + 1) - 1) &, 50] (* _Michael De Vlieger_, Oct 13 2018 *)

%o (Python)

%o for n in range(1,333):

%o print(str((n+1)*(2 ** int.bit_length(int(n))-1)), end=',')

%o (PARI) a(n) = (n+1)*(2^#binary(n)-1); \\ _Michel Marcus_, Jan 08 2015

%Y Cf. A035327, A036044, A070939.

%K nonn,easy,base

%O 1,1

%A _Alex Ratushnyak_, Jan 05 2015