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A115303
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a(n) = n if n < 3, otherwise 3*a(floor(n/3)) + 2 - n mod 3.
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10
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1, 2, 5, 4, 3, 8, 7, 6, 17, 16, 15, 14, 13, 12, 11, 10, 9, 26, 25, 24, 23, 22, 21, 20, 19, 18, 53, 52, 51, 50, 49, 48, 47, 46, 45, 44, 43, 42, 41, 40, 39, 38, 37, 36, 35, 34, 33, 32, 31, 30, 29, 28, 27, 80, 79, 78, 77, 76, 75, 74, 73, 72, 71, 70, 69, 68, 67, 66, 65, 64, 63, 62
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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 ternary representation, then a(n) is the value after replacing all digits d (but not the leading one) with 2-d.
a(n+1) = a(n)-1 unless n = 3^k - 1 or 2*3^k-1 for some k. - Robert Israel, Feb 28 2023
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LINKS
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MAPLE
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a:= proc(n) option remember;
3*procname(floor(n/3))+2 - (n mod 3)
end proc:
a(1):= 1: a(2):= 2:
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CROSSREFS
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KEYWORD
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AUTHOR
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STATUS
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approved
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