A163807 Reverse the order of inner digits (all digits but the first and last) of n written in binary. a(n) = the decimal value of the result.

1, 2, 3, 4, 5, 6, 7, 8, 9, 12, 13, 10, 11, 14, 15, 16, 17, 24, 25, 20, 21, 28, 29, 18, 19, 26, 27, 22, 23, 30, 31, 32, 33, 48, 49, 40, 41, 56, 57, 36, 37, 52, 53, 44, 45, 60, 61, 34, 35, 50, 51, 42, 43, 58, 59, 38, 39, 54, 55, 46, 47, 62, 63, 64, 65, 96, 97, 80, 81, 112, 113, 72

Offset

1,2

Comments

This is a self-inverse permutation of the positive integers.

Links

John Tyler Rascoe, Table of n, a(n) for n = 1..10000

Example

18 in binary is 10010. The inner digits are 001. Reverse these, leaving the first digit (a 1) and the last digit (a 0) untouched, and we have 11000. a(18) is the decimal equivalent of 11000, which is 24.

Mathematica

a[n_]:=FromDigits[Append[Join[{Part[IntegerDigits[n, 2], 1]}, Reverse[Drop[Drop[IntegerDigits[n, 2], 1], -1]]], Part[IntegerDigits[n, 2], -1]], 2]; Join[{1}, Array[a, 71, 2]] (* Stefano Spezia, Jan 14 2023 *)

Crossrefs

Cf. A030101.

Sequence in context: A143265 A109841 A174234 * A118766 A136399 A056167

Adjacent sequences: A163804 A163805 A163806 * A163808 A163809 A163810

Keyword

base,nonn,look

Author

Leroy Quet, Aug 04 2009

Extensions

More terms from R. J. Mathar, Sep 27 2009

Status

approved