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 A141551 Numbers k with property that if d divides k, then tau(tau(d)) also divides k. 3
 1, 2, 4, 6, 12, 24, 36, 48, 60, 72, 84, 96, 108, 120, 132, 144, 156, 180, 192, 204, 228, 240, 252, 276, 288, 300, 324, 348, 360, 372, 396, 444, 468, 480, 492, 516, 564, 576, 588, 600, 612, 636, 684, 708, 720, 732, 804, 828, 840, 852, 876, 900, 948, 960, 972, 996, 1044, 1068 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS tau() = A000005(). LINKS Amiram Eldar, Table of n, a(n) for n = 1..10000 MAPLE with(numtheory); isA141551 := proc(n) local dvs, d; dvs := divisors(n) ; for d in dvs do if not tau(tau(d)) in dvs then RETURN(false): fi; od: RETURN(true); end: t1:=[]; for n from 1 to 60000 do if isA141551(n) then t1:=[op(t1), n]; fi; od: MATHEMATICA aQ[n_] := AllTrue[Divisors[n], Divisible[n, DivisorSigma[0, DivisorSigma[0, #]]] &]; Select[Range[1000], aQ] (* Amiram Eldar, Jul 08 2019 *) CROSSREFS Cf. A000005, A010553, A141586. Sequence in context: A282472 A056795 A141420 * A181804 A094348 A242298 Adjacent sequences:  A141548 A141549 A141550 * A141552 A141553 A141554 KEYWORD nonn AUTHOR N. J. A. Sloane, Sep 12 2008 STATUS approved

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Last modified October 15 05:43 EDT 2019. Contains 328026 sequences. (Running on oeis4.)