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A117968
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Negative part of inverse of A117966; write -n in balanced ternary and then replace (-1)'s with 2's.
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22
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2, 7, 6, 8, 22, 21, 23, 19, 18, 20, 25, 24, 26, 67, 66, 68, 64, 63, 65, 70, 69, 71, 58, 57, 59, 55, 54, 56, 61, 60, 62, 76, 75, 77, 73, 72, 74, 79, 78, 80, 202, 201, 203, 199, 198, 200, 205, 204, 206, 193, 192, 194, 190, 189, 191, 196, 195, 197, 211, 210, 212, 208, 207
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listen;
history;
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OFFSET
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1,1
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REFERENCES
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D. E. Knuth, The Art of Computer Programming. Addison-Wesley, Reading, MA, Vol. 2, pp. 173-175
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LINKS
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FORMULA
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a(1) = 2, a(3n) = 3a(n), a(3n+1) = 3a(n)+2, a(3n-1) = 3a(n)+1.
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EXAMPLE
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-7 in balanced ternary is (-1)1(-1), changing to 212 ternary is 23, so a(7)=23.
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PROG
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(Python)
def a(n):
if n==1: return 2
if n%3==0: return 3*a(n//3)
elif n%3==1: return 3*a((n - 1)//3) + 2
else: return 3*a((n + 1)//3) + 1
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CROSSREFS
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KEYWORD
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base,nonn
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AUTHOR
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STATUS
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approved
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