The On-Line Encyclopedia of Integer Sequences (OEIS)

Revision History for A173438

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A173438

Number of divisors d of number n such that d does not divide sigma(n).
(history; published version)

#16 by N. J. A. Sloane at Mon Oct 09 00:05:02 EDT 2017

STATUS

proposed

approved

#15 by Antti Karttunen at Sun Oct 08 09:21:24 EDT 2017

STATUS

editing

proposed

#14 by Antti Karttunen at Sun Oct 08 09:20:40 EDT 2017

FORMULA

a(n) = tau(n) - tau(gcd(n,sigma(n))). - Antti Karttunen, Oct 08 2017

CROSSREFS

Cf. A000005, A000203, A007691, A009194, A073802, A286570.

STATUS

proposed

editing

#13 by Antti Karttunen at Sun Oct 08 09:18:48 EDT 2017

STATUS

editing

proposed

#12 by Antti Karttunen at Sun Oct 08 09:18:22 EDT 2017

CROSSREFS

Cf. A000005, A000203, A007691, A073802, A286570.

STATUS

proposed

editing

Discussion

Sun Oct 08

09:18

Antti Karttunen: One of the matches of A286570.

#11 by Michael De Vlieger at Sun Oct 08 09:10:12 EDT 2017

STATUS

editing

proposed

#10 by Michael De Vlieger at Sun Oct 08 09:10:10 EDT 2017

MATHEMATICA

Table[DivisorSum[n, 1 &, ! Divisible[DivisorSigma[1, n], #] &], {n, 98}] (* Michael De Vlieger, Oct 08 2017 *)

STATUS

proposed

editing

#9 by Michel Marcus at Sun Oct 08 09:07:25 EDT 2017

STATUS

editing

proposed

#8 by Michel Marcus at Sun Oct 08 09:07:19 EDT 2017

COMMENTS

a(n) = 0 for multiply-perfect numbers (A007691). a(n) = A000005(n) - A073802(n).

FORMULA

a(n) = A000005(n) - A073802(n).

STATUS

proposed

editing

#7 by Antti Karttunen at Sun Oct 08 04:48:43 EDT 2017

STATUS

editing

proposed