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URL: https://oeis.org/A140266

⇱ A140266 - OEIS

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A140266
Inverse permutation to A140265.
3
1, 2, 3, 6, 8, 4, 7, 5, 9, 18, 20, 16, 24, 26, 22, 12, 14, 10, 19, 17, 21, 13, 11, 15, 25, 23, 27, 54, 56, 52, 60, 62, 58, 48, 50, 46, 72, 74, 70, 78, 80, 76, 66, 68, 64, 36, 38, 34, 42, 44, 40, 30, 32, 28, 55, 53, 57, 49, 47, 51, 61, 59, 63, 37, 35, 39, 31, 29, 33, 43, 41, 45
OFFSET
1,2
FORMULA
a(n) = Z->N(A117966(n-1)), where Z->N(z) = 2z if z>0 else 2|z|+1.
PROG
(Scheme) (string-append (define (A140266 n) (Z->N (A117966 (- n 1))))
(define (Z->N n) (if (positive? n) (* n 2) (+ 1 (* 2 (- n))))))
(Python)
def a117966(n):
if n==0: return 0
if n%3==0: return 3*a117966(n/3)
elif n%3==1: return 3*a117966((n - 1)/3) + 1
else: return 3*a117966((n - 2)/3) - 1
def Z(z): return 2*z if z>0 else 2*abs(z) + 1
def a(n): return Z(a117966(n - 1)) # Indranil Ghosh, Jun 07 2017
CROSSREFS
Inverse: A140265. a(n) = A140264(n-1)+1.
Sequence in context: A133441 A086254 A265297 * A140265 A349917 A191453
KEYWORD
nonn,look,hear
AUTHOR
Antti Karttunen, May 19 2008
STATUS
approved