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A137944 Numbers such that the number of composite divisors is a multiple of the number of prime divisors; a(1)=1. 4
2, 3, 4, 5, 7, 8, 9, 11, 13, 16, 17, 19, 23, 25, 27, 29, 31, 32, 36, 37, 41, 43, 47, 49, 53, 59, 61, 64, 67, 71, 73, 79, 81, 83, 89, 97, 100, 101, 103, 107, 109, 113, 120, 121, 125, 127, 128, 131, 137, 139, 144, 149, 151, 157, 163, 167, 168, 169, 173, 179, 181, 191, 193 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

R. Zumkeller, Table of n, a(n) for n = 1..10000

Eric Weisstein's World of Mathematics, Divisor Function

FORMULA

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

MATHEMATICA

aQ[n_] := Divisible[DivisorSigma[0, n] - 1,  PrimeNu[n]]; Select[Range[2, 193], aQ] (* Amiram Eldar, Aug 31 2019 *)

CROSSREFS

Cf. A001221, A055212.

Union of A000961 and A137945.

Sequence in context: A298538 A326534 A046686 * A323306 A325247 A306013

Adjacent sequences:  A137941 A137942 A137943 * A137945 A137946 A137947

KEYWORD

nonn

AUTHOR

Reinhard Zumkeller, Feb 24 2008

STATUS

approved

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Last modified September 19 23:31 EDT 2019. Contains 327207 sequences. (Running on oeis4.)