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A046684 Numbers k such that k and sum of squares of divisors of k are relatively prime. 3
1, 2, 3, 4, 5, 7, 8, 9, 11, 13, 16, 17, 18, 19, 21, 23, 25, 27, 29, 31, 32, 33, 37, 39, 41, 43, 45, 47, 49, 51, 53, 55, 57, 59, 61, 64, 67, 69, 71, 72, 73, 77, 79, 81, 83, 87, 89, 91, 93, 95, 97, 98, 99, 100, 101, 103, 107, 109, 111, 113, 119, 121, 123, 125, 127, 128, 129 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

All even terms are either squares or doubled squares. - Ivan Neretin, Dec 30 2015

The asymptotic density of this sequence is 0 (Dressler, 1974). - Amiram Eldar, Jul 23 2020

LINKS

Ivan Neretin, Table of n, a(n) for n = 1..10000

Robert E. Dressler, On a theorem of Niven, Canadian Mathematical Bulletin, Vol. 17, No. 1 (1974), pp. 109-110.

MATHEMATICA

Select[Range[130], GCD[#, DivisorSigma[2, #]] == 1 &] (* Ivan Neretin, Dec 30 2015 *)

PROG

(PARI) isok(n) = gcd(n, sigma(n, 2)) == 1; \\ Michel Marcus, Jan 10 2017

CROSSREFS

Cf. A001157, A046686, A046687.

Sequence in context: A325394 A062491 A087092 * A082377 A166401 A329131

Adjacent sequences:  A046681 A046682 A046683 * A046685 A046686 A046687

KEYWORD

nonn

AUTHOR

Labos Elemer

STATUS

approved

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Last modified October 22 13:49 EDT 2021. Contains 348170 sequences. (Running on oeis4.)