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%I #24 May 20 2021 10:14:54
%S 0,1,2,1,4,5,2,5,8,9,10,1,4,5,10,13,16,17,18,17,20,21,2,5,8,9,10,17,
%T 20,21,26,29,32,33,34,33,36,37,34,37,40,41,42,1,4,5,10,13,16,17,18,17,
%U 20,21,34,37,40,41,42,49,52,53,58,61,64,65,66,65,68
%N a(n) = 3*n AND n, where AND is the bitwise AND operator.
%C Indices of 1's: A007583(n),
%C indices of 2's: A047849(n+1),
%C indices of 4's: A039301(n+2),
%C indices of 5's: A153643(n+3),
%C indices of 8's: A155701(n+2),
%C indices of 9's: A155701(n+2)+1 = A163868(n+2),
%C indices of 10's: A153643(n+4)+3^((n+1) mod 2),
%C indices of 13's: A039301(n+3)+3,
%C indices of 16's: A039301(n+3)+4,
%C indices of 17's: 17, 19, 27, 49, 51, 91, 177, 179, 347, 689, 691, 1371, 2737, 2739, 5467, 10929, 10931, 21851, 43697, 43699, 87387, 174769, 174771, 349531, 699057, 699059, 1398107, 2796209, 2796211, 5592411, 11184817, 11184819, 22369627, 44739249, 44739251, 89478491, ...
%C indices of 18's: A039301(n+3)+6,
%C n's such that a(n)<3: A005578, except the first term.
%H Alois P. Heinz, <a href="/A213526/b213526.txt">Table of n, a(n) for n = 0..10000</a>
%p a:= proc(n) local i, k, m, r;
%p k, m, r:= n, 3*n, 0;
%p for i from 0 while (m>0 or k>0) do
%p r:= r +2^i* irem(m, 2, 'm') *irem(k, 2, 'k')
%p od; r
%p end:
%p seq(a(n), n=0..100); # _Alois P. Heinz_, Jun 22 2012
%t Table[BitAnd[n, 3*n], {n, 0, 68}] (* _Arkadiusz Wesolowski_, Jun 23 2012 *)
%o (Python)
%o for n in range(99):
%o print(3*n & n, end=',')
%o (PARI) a(n)=bitand(n,3*n) \\ _Charles R Greathouse IV_, Feb 05 2013
%K nonn,base,easy,look
%O 0,3
%A _Alex Ratushnyak_, Jun 13 2012
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