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 A055040 Numbers of the form 3^(2i+1)*(3*j+2). 2
 6, 15, 24, 33, 42, 51, 54, 60, 69, 78, 87, 96, 105, 114, 123, 132, 135, 141, 150, 159, 168, 177, 186, 195, 204, 213, 216, 222, 231, 240, 249, 258, 267, 276, 285, 294, 297, 303, 312, 321, 330, 339, 348, 357, 366, 375, 378, 384, 393, 402, 411 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Numbers not of the form x^2+y^2+3z^2. REFERENCES L. J. Mordell, A new Waring's problem with squares of linear forms, Quart. J. Math., 1 (1930), 276-288 (see p. 283). LINKS Reinhard Zumkeller, Table of n, a(n) for n = 1..10000 FORMULA G.f.: [x(x+2)(x^2+x+1)(x^7+x^3+1)]/(x^11-x^10-x+1) (conjectured). MATHEMATICA max = 500; Select[ Union[ Flatten[ Table[3^(2*i + 1)*(3*j + 2), {i, 0, Ceiling[ Log[max/6]/Log[9]]}, {j, 0, Ceiling[(max/9^i - 6)/9]}]]], # <= max &] (* Jean-François Alcover, Oct 13 2011 *) PROG (Haskell) a055040 n = a055040_list !! (n-1) a055040_list = map (* 3) a055048_list -- Reinhard Zumkeller, Apr 07 2012 CROSSREFS Equals 3*A055048(n). Sequence in context: A227229 A274319 A043477 * A017233 A122709 A052220 Adjacent sequences:  A055037 A055038 A055039 * A055041 A055042 A055043 KEYWORD nonn,nice AUTHOR N. J. A. Sloane, Jun 01 2000 STATUS approved

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