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A115304
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a(n) = n if n < 4, otherwise 4*a(floor(n/4)) + 3 - n mod 4.
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10
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1, 2, 3, 7, 6, 5, 4, 11, 10, 9, 8, 15, 14, 13, 12, 31, 30, 29, 28, 27, 26, 25, 24, 23, 22, 21, 20, 19, 18, 17, 16, 47, 46, 45, 44, 43, 42, 41, 40, 39, 38, 37, 36, 35, 34, 33, 32, 63, 62, 61, 60, 59, 58, 57, 56, 55, 54, 53, 52, 51, 50, 49, 48, 127, 126, 125, 124, 123, 122, 121
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OFFSET
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1,2
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COMMENTS
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Self-inverse permutation of the natural numbers.
If n is written in base-4 representation, then a(n) is the value after replacing all digits d (except for the leading one) by 3-d.
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LINKS
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FORMULA
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MATHEMATICA
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A115304[n_] := FromDigits[MapAt[3 - # &, IntegerDigits[n, 4], 2;; ], 4];
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CROSSREFS
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KEYWORD
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nonn,base
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AUTHOR
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STATUS
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approved
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