A141551 - OEIS

A141551

Numbers k with property that if d divides k, then tau(tau(d)) also divides k.

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

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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: A095416 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