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A328951 Numbers m such that sigma(m) + tau(m) = 3m. 0
60, 5472, 2500704 (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, ...

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

10^13 < a(4) <= 24361213461200. 808989640739424 is also a term. - Giovanni Resta, Nov 14 2019

LINKS

Table of n, a(n) for n=1..3.

EXAMPLE

Number 60 is in the sequence 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 A303790

Adjacent sequences:  A328948 A328949 A328950 * A328952 A328953 A328954

KEYWORD

nonn,bref,more

AUTHOR

Jaroslav Krizek, Nov 10 2019

STATUS

approved

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Last modified February 21 04:39 EST 2020. Contains 332086 sequences. (Running on oeis4.)