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.

0, 1, 11, 11, 101, 101, 1001, 111, 1001, 1001, 1111, 11011, 1111, 11011, 10101, 1111, 10001, 10001, 11011, 1100011, 1100011, 10101, -1, 111111, 11011, 1100011, -1, 11011, -1, 111111, 101101, 11111, 100001, 100001, 110011, -1, 101101, -1, 111111, 1100011, 101101, -1, 111111, 1100011, 1100011

Offset: 0

Author

Klaus Brockhaus, Jun 06 2001

Keywords

• base
• easy
• sign

Comments

The analog of A033865 in base 2.

Examples

			23: 10111 -> 10111 + 11101 = 110100 -> 110100 + 1011 = 111111, so a(23) = 111111.
		

Links

• Klaus Brockhaus, On the'Reverse and Add!' algorithm in base 2
• Index entries for sequences related to Reverse and Add!

Crossrefs

Cf. A033865, A062129, A062130, A058042.

Programs

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;

Mathematica

limit = 10^4; (* Assumes that there is no palindrome if none is found before "limit" iterations *)
BaseForm[Table[np = n; i = 0;
  While[np != IntegerReverse[np, 2] && i < limit,
   np = np + IntegerReverse[np, 2]; i++];
If[i >= limit, -1, np], {n, 0, 44}], 2] (* Robert Price, Oct 14 2019 *)