A375183 In the binary expansion of n, complement bits at even positions and to the right of a 1 (the most significant bit corresponding to position 1).
0, 1, 3, 2, 6, 7, 4, 5, 12, 13, 15, 14, 8, 9, 11, 10, 24, 25, 26, 27, 30, 31, 28, 29, 16, 17, 18, 19, 22, 23, 20, 21, 48, 49, 51, 50, 52, 53, 55, 54, 60, 61, 63, 62, 56, 57, 59, 58, 32, 33, 35, 34, 36, 37, 39, 38, 44, 45, 47, 46, 40, 41, 43, 42, 96, 97, 98, 99
Offset: 0
Examples
For n = 9: the binary expansion of 9 is "1001": the bit at position 2 (0) sits to the right of a 1 so we complement it, the bit at position 4 (1) sits to the right of a 0 so we keep it; the binary expansion of a(9) is "1101" and a(9) = 13.
Links
Programs
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PARI
a(n) = { my (b = binary(n)); forstep (k = 2, #b, 2, if (b[k-1], b[k] = 1-b[k];);); fromdigits(b, 2); }
Formula
a(floor(n/2)) = floor(a(n)/2).
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