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A365458
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The largest power of 3 that is less than or equal to n.
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2
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1, 1, 3, 3, 3, 3, 3, 3, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 81, 81, 81, 81, 81
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OFFSET
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1,3
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LINKS
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FORMULA
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EXAMPLE
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a(2) = 1 because 3^0 = 1 <= 2.
a(3) = 3 because 3^1 = 3 <= 3.
a(4) = 3 because 3^1 = 3 <= 4.
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MATHEMATICA
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PROG
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(PARI) A365458(n) = if(1==n, n, my(k=0); while((3^k) < n, k++); if((3^k) > n, k--); (3^k));
(Python)
kmin, kmax = 0, 1
while 3**kmax <= n:
kmax <<= 1
while True:
kmid = kmax+kmin>>1
if 3**kmid > n:
kmax = kmid
else:
kmin = kmid
if kmax-kmin <= 1:
break
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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