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URL: https://oeis.org/A389907

⇱ A389907 - OEIS

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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.
5
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.
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
KEYWORD
nonn,base,easy
AUTHOR
Antti Karttunen, Nov 08 2025
STATUS
approved