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A054020 Chowla's function of n is not divisible by the number of proper divisors of n. 2
6, 9, 10, 15, 16, 20, 21, 22, 25, 28, 30, 33, 34, 36, 39, 42, 44, 45, 46, 48, 49, 50, 51, 54, 55, 57, 58, 60, 64, 68, 69, 70, 72, 75, 76, 78, 80, 81, 82, 84, 85, 87, 91, 93, 94, 96, 98, 99, 100, 102, 105, 106, 108, 111, 114, 115, 116, 117, 118, 120, 121, 123, 124, 126 (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..500)];

MATHEMATICA

Select[Range[2, 150], !Divisible[DivisorSigma[1, #]-#-1, DivisorSigma[ 0, #]- 1]&] (* Harvey P. Dale, May 27 2014 *)

CROSSREFS

Complement is A054021.

Cf. A032741, A048050, A054015.

Sequence in context: A145311 A328244 A037198 * A121014 A153519 A020219

Adjacent sequences:  A054017 A054018 A054019 * A054021 A054022 A054023

KEYWORD

nonn

AUTHOR

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

STATUS

approved

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Last modified December 8 17:01 EST 2021. Contains 349596 sequences. (Running on oeis4.)