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 A281228 Expansion of (Sum_{k>=0} x^(3^k))^2 [even terms only]. 1
 0, 1, 2, 1, 0, 2, 2, 0, 0, 1, 0, 0, 0, 0, 2, 2, 0, 0, 2, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 2, 2, 0, 0, 2, 0, 0, 0, 0, 0, 0, 0, 0, 2, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 COMMENTS Number of ways to write 2n as an ordered sum of two powers of 3. First bisection of self-convolution of characteristic function of powers of 3. LINKS FORMULA G.f.: (Sum_{k>=0} x^(3^k))^2 [even terms only]. EXAMPLE G.f. = x^2 + 2*x^4 + x^6 + 2*x^10 + 2*x^12 + x^18 + 2*x^28 + 2*x^30 + 2*x^36 + ... a(2) = 2 because we have [3, 1] and [1, 3]. MATHEMATICA Take[CoefficientList[Series[Sum[x^3^k, {k, 0, 15}]^2, {x, 0, 260}], x], {1, -1, 2}] CROSSREFS Cf. A000244, A055235, A073267, A078932. Sequence in context: A240808 A263142 A025253 * A284575 A112178 A134663 Adjacent sequences:  A281225 A281226 A281227 * A281229 A281230 A281231 KEYWORD nonn AUTHOR Ilya Gutkovskiy, Jan 18 2017 STATUS approved

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Last modified May 18 08:21 EDT 2021. Contains 343995 sequences. (Running on oeis4.)