A328951 - OEIS

The OEIS is supported by the many generous donors to the OEIS Foundation.

Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).

Other ways to Give

A328951

Numbers m such that sigma(m) + tau(m) = 3m.

60, 5472, 2500704, 24361213461200

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,1

COMMENTS

Abundant numbers m with abundance A(m) = m - tau(m) = A049820(m), where A049820(n) is the number of non-divisors of n.

Subsequence of A056076.

Corresponding values of A(m) = m - tau(m): 48, 5436, 2500632, ...

4 is the only number m with deficiency D(m) = m - tau(m).

808989640739424 is also a term. - Giovanni Resta, Nov 14 2019

LINKS

Table of n, a(n) for n=1..4.

EXAMPLE

60 is a term because sigma(60) + tau(60) = 3*60; 168 + 12 = 180 = 3*60.

MATHEMATICA

Select[Range[3*10^6], DivisorSigma[0, #] + DivisorSigma[1, #] == 3# &] (* Amiram Eldar, Nov 10 2019 *)

PROG

(Magma) [m: m in [1..10^7] | SumOfDivisors(m) - 2*m eq m - NumberOfDivisors(m)];

(PARI) isok(m) = my(f=factor(m)); sigma(f) + numdiv(m) == 3*m; \\ Michel Marcus, Nov 13 2019

CROSSREFS

Cf. A000005, A000203, A033880, A049820, A056076.

Cf. A083874 (numbers m such that sigma(m) + tau(m) = 2m).

Cf. A011251 (numbers m such that sigma(m) + phi(m) = 3m).

Cf. A329104 (numbers m with abundance A(m) = tau(m)).

Sequence in context: A084274 A289307 A091032 * A178785 A091753 A336629

Adjacent sequences: A328948 A328949 A328950 * A328952 A328953 A328954

KEYWORD

nonn,more

AUTHOR

Jaroslav Krizek, Nov 10 2019

EXTENSIONS

a(4) from Martin Ehrenstein, Jul 25 2023

STATUS

approved