

A163327


Selfinverse permutation of integers: swap the odd and evenpositioned digits in the ternary expansion of n, then convert back to decimal.


11



0, 3, 6, 1, 4, 7, 2, 5, 8, 27, 30, 33, 28, 31, 34, 29, 32, 35, 54, 57, 60, 55, 58, 61, 56, 59, 62, 9, 12, 15, 10, 13, 16, 11, 14, 17, 36, 39, 42, 37, 40, 43, 38, 41, 44, 63, 66, 69, 64, 67, 70, 65, 68, 71, 18, 21, 24, 19, 22, 25, 20, 23, 26, 45, 48, 51, 46, 49, 52, 47, 50, 53
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OFFSET

0,2


LINKS



FORMULA



EXAMPLE

11 in ternary base (A007089) is written as '(000...)102' (... + 0*27 + 1*9 + 0*3 + 2), which results '1020' = 1*27 + 0*9 + 2*3 + 0 = 33, when the odd and evenpositioned digits are swapped, thus a(11) = 33.


PROG

(Python)
from sympy.ntheory import digits
def a(n):
d = digits(n, 3)[1:]
return sum(3**(i+(12*(i&1)))*di for i, di in enumerate(d[::1]))


CROSSREFS



KEYWORD



AUTHOR



EXTENSIONS



STATUS

approved



