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 A055048 Numbers of the form 9^i*(3*j+2). 6
 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 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS 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 LINKS Reinhard Zumkeller, Table of n, a(n) for n = 1..10000 L. J. Mordell, A new Waring's problem with squares of linear forms, Quart. J. Math., 1 (1930), 276-288 (see p. 283). FORMULA a(n) = A055040(n)/3. - Peter Munn, May 17 2020 MATHEMATICA 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 *) PROG (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 -- Reinhard Zumkeller, Apr 07 2012 (PARI) is(n)=n/=9^valuation(n, 9); n%3==2 \\ Charles R Greathouse IV and V. Raman, Dec 19 2013 CROSSREFS Intersection of A007417 and A189716. Complement of A055047 with respect to A007417. Complement of A055041 with respect to A189716. Cf. A007913, A055040. Sequence in context: A022842 A189525 A189369 * A045930 A140099 A276385 Adjacent sequences:  A055045 A055046 A055047 * A055049 A055050 A055051 KEYWORD nonn AUTHOR N. J. A. Sloane, Jun 01 2000 STATUS approved

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Last modified May 14 08:44 EDT 2021. Contains 343879 sequences. (Running on oeis4.)