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A153151
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Rotated binary decrementing: For n<2 a(n) = n, if n=2^k, a(n) = 2*n-1, otherwise a(n) = n-1.
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8
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0, 1, 3, 2, 7, 4, 5, 6, 15, 8, 9, 10, 11, 12, 13, 14, 31, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 63, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 127, 64, 65, 66, 67, 68, 69
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OFFSET
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0,3
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COMMENTS
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Without the initial 0, a(n) is the lexicographically minimal sequence of distinct positive integers such that all values of a(n) mod n are distinct and nonnegative. - Ivan Neretin, Apr 27 2015
A002487(n)/A002487(n+1), n > 0, runs through all the reduced nonnegative rationals exactly once. A002487 is the Stern's sequence. Permutation from denominators (A002487(n+1))
1 2 1 3 2 3 1 4 3 5 2 5 3 4 1
where labels are
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
1 1 2 1 3 2 3 1 4 3 5 2 5 3 4
where changed labels are
1 3 2 7 4 5 6 15 8 9 10 11 12 13 14
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LINKS
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FORMULA
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MAPLE
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a := n -> if n < 2 then n elif convert(convert(n, base, 2), `+`) = 1 then 2*n-1 else n-1 fi: seq(a(n), n=0..70); # Peter Luschny, Jul 16 2016
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MATHEMATICA
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Table[Which[n < 2, n, IntegerQ[Log[2, n]], 2 n - 1, True, n - 1], {n, 0, 70}] (* Michael De Vlieger, Apr 27 2015 *)
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PROG
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(MIT/GNU Scheme) (define (A153151 n) (cond ((< n 2) n) ((pow2? n) (- (* 2 n) 1)) (else (- n 1))))
(define (pow2? n) (and (> n 0) (zero? (A004198bi n (- n 1)))))
(Python)
def ok(n): return n&(n - 1)==0
def a(n): return n if n<2 else 2*n - 1 if ok(n) else n - 1 # Indranil Ghosh, Jun 09 2017
(R)
nmax <- 126 # by choice
a <- c(1, 3, 2)
for(n in 3:nmax) a[n+1] <- n
for(m in 0:floor(log2(nmax))) a[2^m] <- 2^(m+1) - 1
a <- c(0, a)
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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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