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A137945 Non-prime-powers such that the number of composite divisors is a multiple of the number of prime divisors. 3
36, 100, 120, 144, 168, 196, 225, 264, 270, 280, 312, 324, 378, 400, 408, 440, 441, 456, 484, 520, 552, 576, 594, 616, 676, 680, 696, 702, 728, 744, 750, 760, 784, 888, 918, 920, 945, 952, 960, 984, 1026, 1032, 1064, 1089, 1128, 1144, 1156, 1160, 1225, 1240 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Amiram Eldar, Table of n, a(n) for n = 1..10000 (terms 1..1000 from Reinhard Zumkeller)

Eric Weisstein's World of Mathematics, Divisor Function

FORMULA

A055212(a(n)) mod A001221(a(n)) = 0.

EXAMPLE

A055212(120) = #{4,6,8,10,12,15,20,24,30,40,60,120} = 12 = 4*A001221(120) = 4*#{2,3,5} = 12, therefore 120 is a term.

MATHEMATICA

aQ[n_] := (omega = PrimeNu[n]) > 1 && Divisible[DivisorSigma[0, n] - 1, omega]; Select[Range[2, 1240], aQ] (* Amiram Eldar, Aug 31 2019 *)

CROSSREFS

Cf. A001221, A055212.

Intersection of A024619 and A137944.

Sequence in context: A260007 A306213 A114819 * A250812 A072413 A131605

Adjacent sequences:  A137942 A137943 A137944 * A137946 A137947 A137948

KEYWORD

nonn

AUTHOR

Reinhard Zumkeller, Feb 24 2008

STATUS

approved

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Last modified October 18 07:42 EDT 2019. Contains 328146 sequences. (Running on oeis4.)