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A055048
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Numbers of the form 9^i*(3*j+2).
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7
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2, 5, 8, 11, 14, 17, 18, 20, 23, 26, 29, 32, 35, 38, 41, 44, 45, 47, 50, 53, 56, 59, 62, 65, 68, 71, 72, 74, 77, 80, 83, 86, 89, 92, 95, 98, 99, 101, 104, 107, 110, 113, 116, 119, 122, 125, 126, 128, 131, 134, 137, 140, 143, 146, 149, 152, 153, 155
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OFFSET
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1,1
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COMMENTS
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The numbers not of the form x^2+3y^2+3z^2.
Numbers whose squarefree part is congruent to 2 modulo 3. - Peter Munn, May 17 2020
The asymptotic density of this sequence is 3/8. - Amiram Eldar, Mar 08 2021
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LINKS
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FORMULA
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MATHEMATICA
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max = 200; Select[ Union[ Flatten[ Table[ 9^i*(3*j + 2), {i, 0, Ceiling[Log[max]/Log[9]]}, {j, 0, Ceiling[( max/9^i - 2)/3]}]]], # <= max &] (* Jean-François Alcover, Oct 13 2011 *)
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PROG
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(Haskell)
a055048 n = a055048_list !! (n-1)
a055048_list = filter (s 0) [1..] where
s t u | m > 0 = even t && m == 2
| m == 0 = s (t + 1) u' where (u', m) = divMod u 3
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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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