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 A143348 a(n) = -(-1)^n times sum of divisors of n. 3
 1, -3, 4, -7, 6, -12, 8, -15, 13, -18, 12, -28, 14, -24, 24, -31, 18, -39, 20, -42, 32, -36, 24, -60, 31, -42, 40, -56, 30, -72, 32, -63, 48, -54, 48, -91, 38, -60, 56, -90, 42, -96, 44, -84, 78, -72, 48, -124, 57, -93, 72, -98, 54, -120, 72, -120, 80, -90, 60, -168, 62, -96, 104, -127, 84, -144, 68, -126, 96 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS Indranil Ghosh, Table of n, a(n) for n = 1..10000 László Tóth, Alternating sums concerning multiplicative arithmetic functions, arXiv preprint arXiv:1608.00795 [math.NT], 2016. FORMULA a(n) is multiplicative with a(2^e) = 1 - 2^(e+1) if e > 0, a(p^e) = (p^(e+1) - 1) / (p - 1) if p > 2. G.f.: Sum_{k>0} k * -(-x)^k / (1 - (-x)^k) = Sum_{k>0} -(-x)^k / (1 - (-x)^k)^2. Dirichlet g.f.: zeta(s) * zeta(s-1) * (1 - 6 / 2^s + 4 / 4^s). EXAMPLE q - 3*q^2 + 4*q^3 - 7*q^4 + 6*q^5 - 12*q^6 + 8*q^7 - 15*q^8 + 13*q^9 + ... MATHEMATICA Table[-(-1)^n*DivisorSigma[1, n], {n, 69}] (* Michael De Vlieger, Aug 19 2017 *) PROG (PARI) {a(n) = if( n<1, 0, -(-1)^n * sigma(n))} CROSSREFS -(-1)^n * A000203(n) = a(n). A143337(n) = 24 * a(n) unless n=0. Sequence in context: A097863 A287926 A097012 * A000203 A324545 A003979 Adjacent sequences:  A143345 A143346 A143347 * A143349 A143350 A143351 KEYWORD sign,mult AUTHOR Michael Somos, Aug 09 2008 STATUS approved

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Last modified November 28 07:44 EST 2020. Contains 338702 sequences. (Running on oeis4.)