A389907 a(n) = min(n, A054429(n)), where A054429 list each block of 2^n numbers (from 2^n to 2^(n+1) - 1) in reverse order.

1, 2, 2, 4, 5, 5, 4, 8, 9, 10, 11, 11, 10, 9, 8, 16, 17, 18, 19, 20, 21, 22, 23, 23, 22, 21, 20, 19, 18, 17, 16, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 47, 46, 45, 44, 43, 42, 41, 40, 39, 38, 37, 36, 35, 34, 33, 32, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82

Offset

1,2

Comments

Each subsection from 2^n to 2^(n+1) - 1 is palindromic.

Links

Antti Karttunen, Table of n, a(n) for n = 1..16383

Index entries for sequences related to binary expansion of n.

Mathematica

A389907[n_] := Min[n, 3*2^(BitLength[n] - 1) - n - 1];
Array[A389907, 100] (* Paolo Xausa, Feb 08 2026 *)

Prog

(PARI)
A054429(n) = ((3<<#binary(n\2))-n-1);
A389907(n) = min(n, A054429(n));

Crossrefs

Cf. A054429.

Cf. also A331166.

Sequence in context: A225840 A361645 A319409 * A122543 A375421 A334149

Adjacent sequences: A389904 A389905 A389906 * A389908 A389909 A389910

Keyword

nonn,base,easy

Author

Antti Karttunen, Nov 08 2025

Status

approved