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A054021 Numbers n such that Chowla's function of n is divisible by the number of proper divisors of n. 2
2, 3, 4, 5, 7, 8, 11, 12, 13, 14, 17, 18, 19, 23, 24, 26, 27, 29, 31, 32, 35, 37, 38, 40, 41, 43, 47, 52, 53, 56, 59, 61, 62, 63, 65, 66, 67, 71, 73, 74, 77, 79, 83, 86, 88, 89, 90, 92, 95, 97, 101, 103, 104, 107, 109, 110, 112, 113, 119, 122, 125, 127, 128, 131, 134, 136 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Chowla's function (A048050) = sum of divisors of n except 1 and n.

LINKS

Amiram Eldar, Table of n, a(n) for n = 1..10000

MAPLE

with(numtheory):

[seq(`if`((sigma(i)-i-1) mod (tau(i)-1)=0, i, print( )), i=2..1000)];

MATHEMATICA

Select[Range[2, 150], Divisible[DivisorSigma[1, #]-1-#, DivisorSigma[ 0, #]-1]&] (* Harvey P. Dale, Aug 13 2018 *)

CROSSREFS

Complement is A054020.

Cf. A032741, A048050, A054015.

Sequence in context: A214036 A100289 A255130 * A066191 A166159 A169693

Adjacent sequences:  A054018 A054019 A054020 * A054022 A054023 A054024

KEYWORD

nonn

AUTHOR

Asher Auel (asher.auel(AT)reed.edu), Jan 19 2000

STATUS

approved

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Last modified April 17 23:03 EDT 2021. Contains 343071 sequences. (Running on oeis4.)