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A331667 Numbers m with a divisor d such that tau(d)^d = m. 0
1, 4, 19683, 65536, 2176782336, 101559956668416, 7958661109946400884391936 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Corresponding values of divisors d and tau(d) are 1, 2, 9, 8, 12, 18, 32, ..., and 1, 2, 3, 4, 6, 6, 6, ..., respectively.

a(8) = 2^144*3^72 = 12^72 is too large to be included in Data. - Giovanni Resta, Feb 28 2020

LINKS

Table of n, a(n) for n=1..7.

EXAMPLE

19683 is a term because 3^9 = 19683; 9 divides 19683, tau(9) = 3.

MATHEMATICA

seqQ[n_] := AnyTrue[Divisors[n], DivisorSigma[0, #]^# == n &]; Select[Range[70000], seqQ] (* Amiram Eldar, Feb 28 2020 *)

PROG

(MAGMA) [n: n in [1..100000] | #[d: d in Divisors(n) | NumberOfDivisors(d)^d eq n] ge 1]

(PARI) isok(m) = fordiv(m, d, if (numdiv(d)^d == m, return (1)); ); \\ Michel Marcus, Mar 07 2020

CROSSREFS

Cf. A236284 (tau(n)^n).

Cf. A000005, A332646.

Sequence in context: A265215 A070157 A003556 * A053015 A089210 A203037

Adjacent sequences:  A331664 A331665 A331666 * A331668 A331669 A331670

KEYWORD

nonn

AUTHOR

Jaroslav Krizek, Feb 28 2020

EXTENSIONS

More terms from Giovanni Resta, Feb 28 2020

STATUS

approved

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Last modified November 28 16:04 EST 2021. Contains 349413 sequences. (Running on oeis4.)