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 A255347 a(n) = n * (1 - (-1)^(n/4) / 4) if n divisible by 4, a(n) = n otherwise. 1
 0, 1, 2, 3, 5, 5, 6, 7, 6, 9, 10, 11, 15, 13, 14, 15, 12, 17, 18, 19, 25, 21, 22, 23, 18, 25, 26, 27, 35, 29, 30, 31, 24, 33, 34, 35, 45, 37, 38, 39, 30, 41, 42, 43, 55, 45, 46, 47, 36, 49, 50, 51, 65, 53, 54, 55, 42, 57, 58, 59, 75, 61, 62, 63, 48, 65, 66 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 LINKS G. C. Greubel, Table of n, a(n) for n = 0..2500 Index entries for linear recurrences with constant coefficients, signature (2,-1,0,-2,4,-2,0,-1,2,-1). FORMULA Euler transform of length 10 sequence [2, 0, 1, -2, 1, -1, 0, 2, 0, -1]. a(n) is multiplicative with a(2) = 2, a(4) = 5, a(2^e) = 3*2^(e-1) if e>2, a(p^e) = p^e otherwise. G.f.: f(x) - f(-x^4) where f(x) := x / (1 - x)^2. G.f.: x * (1 + x^3) * (1 + x^5) / ((1 - x)^2 * (1 + x^4)^2). a(n) = -a(-n) for all n in Z. EXAMPLE G.f. = x + 2*x^2 + 3*x^3 + 5*x^4 + 5*x^5 + 6*x^6 + 7*x^7 + 6*x^8 + 9*x^9 + ... MATHEMATICA a[ n_] := n {1, 1, 1, 5/4, 1, 1, 1, 3/4}[[Mod[ n, 8, 1]]]; a[ n_] := n If[ Divisible[ n, 4], 1 - (-1)^(n/4) / 4, 1]; LinearRecurrence[{2, -1, 0, -2, 4, -2, 0, -1, 2, -1}, {0, 1, 2, 3, 5, 5, 6, 7, 6, 9}, 70] (* Harvey P. Dale, Jul 28 2018 *) CoefficientList[Series[x*(1+x^3)*(1+x^5)/((1-x)^2*(1+x^4)^2), {x, 0, 60}], x] (* G. C. Greubel, Aug 02 2018 *) PROG (PARI) {a(n) = n * if( n%4, 1, 1 - (-1)^(n/4) / 4)}; (PARI) {a(n) = n * [3/4, 1, 1, 1, 5/4, 1, 1, 1][n%8 + 1]}; (PARI) x='x+O('x^60); concat([0], Vec(x*(1+x^3)*(1+x^5)/((1-x)^2*(1 + x^4)^2))) \\ G. C. Greubel, Aug 02 2018 (MAGMA) m:=60; R:=PowerSeriesRing(Integers(), m); [0] cat Coefficients(R!(x*(1+x^3)*(1+x^5)/((1-x)^2*(1+x^4)^2))); // G. C. Greubel, Aug 02 2018 CROSSREFS Sequence in context: A169787 A165959 A111164 * A029910 A063677 A078903 Adjacent sequences:  A255344 A255345 A255346 * A255348 A255349 A255350 KEYWORD nonn,mult,easy AUTHOR Michael Somos, May 04 2015 STATUS approved

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Last modified November 26 09:38 EST 2020. Contains 338639 sequences. (Running on oeis4.)