cp's OEIS Frontend

A062128 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.

%I A062128 #17 Apr 19 2025 18:08:00
%S A062128 0,1,11,11,101,101,1001,111,1001,1001,1111,11011,1111,11011,10101,
%T A062128 1111,10001,10001,11011,1100011,1100011,10101,-1,111111,11011,1100011,
%U A062128 -1,11011,-1,111111,101101,11111,100001,100001,110011,-1,101101,-1,111111,1100011,101101,-1,111111,1100011,1100011
%N A062128 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 A062128 The analog of A033865 in base 2.
%H A062128 Klaus Brockhaus, <a href="/A058042/a058042.txt">On the'Reverse and Add!' algorithm in base 2</a>
%H A062128 <a href="/index/Res#RAA">Index entries for sequences related to Reverse and Add!</a>
%e A062128 23: 10111 -> 10111 + 11101 = 110100 -> 110100 + 1011 = 111111, so a(23) = 111111.
%t A062128 limit = 10^4; (* Assumes that there is no palindrome if none is found before "limit" iterations *)
%t A062128 BaseForm[Table[np = n; i = 0;
%t A062128   While[np != IntegerReverse[np, 2] && i < limit,
%t A062128    np = np + IntegerReverse[np, 2]; i++];
%t A062128 If[i >= limit, -1, np], {n, 0, 44}], 2] (* _Robert Price_, Oct 14 2019 *)
%o A062128 (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 A062128 Cf. A033865, A062129, A062130, A058042.
%K A062128 base,easy,sign
%O A062128 0,3
%A A062128 _Klaus Brockhaus_, Jun 06 2001