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%I #12 Oct 14 2019 21:09:09
%S 0,1,11,11,101,101,1001,111,1001,1001,1111,11011,1111,11011,10101,
%T 1111,10001,10001,11011,1100011,1100011,10101,-1,111111,11011,1100011,
%U -1,11011,-1,111111,101101,11111,100001,100001,110011,-1,101101,-1,111111,1100011,101101,-1,111111,1100011,1100011
%N In base 2: start with n; if palindrome, stop; otherwise add to itself with digits reversed; a(n) gives palindrome at which it stops, or -1 if no palindrome is ever reached.
%C The analog of A033865 in base 2.
%H <a href="/index/Res#RAA">Index entries for sequences related to Reverse and Add!</a>
%H Klaus Brockhaus, <a href="/A058042/a058042.txt">On the'Reverse and Add!' algorithm in base 2</a>
%e 23: 10111 -> 10111 + 11101 = 110100 -> 110100 + 1011 = 111111, so a(23) = 111111.
%t limit = 10^4; (* Assumes that there is no palindrome if none is found before "limit" iterations *)
%t BaseForm[Table[np = n; i = 0;
%t While[np != IntegerReverse[np, 2] && i < limit,
%t np = np + IntegerReverse[np, 2]; i++];
%t If[i >= limit, -1, np], {n, 0, 44}], 2] (* _Robert Price_, Oct 14 2019 *)
%o (ARIBAS): stop := 500; for k := 0 to 60 do c := 0; m := k; rev := bit_reverse(m); while m <> rev and c < stop do inc(c); m := m + rev; rev := bit_reverse(m); end; if c < stop then bit_write(m); else write(-1); end; write(" "); end;.
%Y Cf. A033865, A062129, A062130, A058042.
%K base,easy,sign
%O 0,3
%A _Klaus Brockhaus_, Jun 06 2001
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