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 A339667 Number of nonempty subsets of divisors of n having a common factor > 1. 0
 0, 1, 1, 3, 1, 5, 1, 7, 3, 5, 1, 19, 1, 5, 5, 15, 1, 19, 1, 19, 5, 5, 1, 71, 3, 5, 7, 19, 1, 37, 1, 31, 5, 5, 5, 111, 1, 5, 5, 71, 1, 37, 1, 19, 19, 5, 1, 271, 3, 19, 5, 19, 1, 71, 5, 71, 5, 5, 1, 347, 1, 5, 19, 63, 5, 37, 1, 19, 5, 37, 1, 703, 1, 5, 19, 19, 5, 37, 1, 271 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,4 LINKS FORMULA a(n) = -Sum_{d|n, d < n} mu(n/d) * (2^tau(d) - 1), where tau = A000005. a(n) = A100587(n) - A076078(n). a(p) = 1 for p prime. EXAMPLE a(12) = 19 subsets: {2}, {3}, {4}, {6}, {12}, {2, 4}, {2, 6}, {2, 12}, {3, 6}, {3, 12}, {4, 6}, {4, 12}, {6, 12}, {2, 4, 6}, {2, 4, 12}, {2, 6, 12}, {3, 6, 12}, {4, 6, 12} and {2, 4, 6, 12}. MATHEMATICA Table[-DivisorSum[n, MoebiusMu[n/#] (2^DivisorSigma[0, #] - 1) &, # < n &], {n, 80}] CROSSREFS Cf. A000005, A027750, A076078, A100587, A109511. Sequence in context: A093411 A147088 A340083 * A322993 A118402 A122383 Adjacent sequences:  A339664 A339665 A339666 * A339668 A339669 A339670 KEYWORD nonn AUTHOR Ilya Gutkovskiy, Dec 12 2020 STATUS approved

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Last modified May 12 11:51 EDT 2021. Contains 343821 sequences. (Running on oeis4.)