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a(n) is the concatenation of n and 3n in binary.
3

%I #16 Sep 06 2014 00:49:25

%S 0,7,22,57,76,95,210,245,280,315,350,737,804,871,938,1005,1072,1139,

%T 1206,1273,1340,1407,2882,3013,3144,3275,3406,3537,3668,3799,3930,

%U 4061,4192,4323,4454,4585,4716,4847,4978,5109,5240,5371,5502,11137,11396,11655

%N a(n) is the concatenation of n and 3n in binary.

%H Alois P. Heinz, <a href="/A246831/b246831.txt">Table of n, a(n) for n = 0..10000</a>

%F a(n) = A246830(2n,n).

%e a(0) = (0|0)_2 = 0.

%e a(1) = (1|11)_2 = 7.

%e a(2) = (10|110)_2 = 22.

%e a(3) = (11|1001)_2 = 57.

%e a(4) = (100|1100)_2 = 76.

%e a(5) = (101|1111)_2 = 95.

%p f:= proc(i, j) local r, h, k; r:=0; h:=0; k:=j;

%p while k>0 do r:=r+2^h*irem(k, 2, 'k'); h:=h+1 od; k:=i;

%p while k>0 do r:=r+2^h*irem(k, 2, 'k'); h:=h+1 od; r

%p end:

%p a:= n-> f(n, 3*n):

%p seq(a(n), n=0..60);

%o (Python)

%o def A246831(n):

%o ....return int(bin(n)[2:]+bin(3*n)[2:],2) # _Chai Wah Wu_, Sep 05 2014

%Y Cf. A246830. Column k=3 of A246834.

%K nonn,base

%O 0,2

%A _Alois P. Heinz_, Sep 04 2014