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A039819 Number of divisors of n-th refactorable number (A033950(n)). 7
1, 2, 4, 3, 6, 6, 8, 9, 8, 8, 12, 12, 10, 12, 8, 12, 8, 12, 8, 12, 8, 8, 12, 18, 8, 12, 9, 12, 8, 20, 8, 18, 12, 18, 8, 8, 8, 12, 24, 12, 8, 16, 18, 8, 9, 12, 14, 18, 18, 8, 24, 8, 12, 24, 12, 8, 20, 12, 8, 8, 24, 18, 5, 8, 12, 16, 8, 24, 18, 12, 8, 30, 12, 8, 24, 12, 8, 8, 18, 12, 8, 24, 8 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

A number n is refactorable if the number of divisors of n divides n.

LINKS

Amiram Eldar, Table of n, a(n) for n = 1..10000

FORMULA

A033950(n)/a(n) = A036762(n).

a(n) =  A000005(A033950(n)). - Omar E. Pol, Jan 17 2017

MATHEMATICA

fQ[n_] := Mod[n, DivisorSigma[0, n]] == 0; DivisorSigma[0, # ] & /@ Select[ Range[1000], fQ[ # ] &] (* Robert G. Wilson v *)

PROG

(MAGMA) v:=[ n: n in [1..900] | n mod NumberOfDivisors(n) eq 0 ]; [NumberOfDivisors(v[i]): i in [1..#v]]; // Marius A. Burtea, Jul 02 2019

CROSSREFS

Cf. A033950, A000005, A036762, A281188.

Sequence in context: A309131 A162953 A235451 * A242424 A232271 A194277

Adjacent sequences:  A039816 A039817 A039818 * A039820 A039821 A039822

KEYWORD

nonn

AUTHOR

N. J. A. Sloane.

EXTENSIONS

More terms from Robert G. Wilson v, Oct 29 2005

Minor edits by Franklin T. Adams-Watters, Jan 17 2017

STATUS

approved

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Last modified September 25 12:57 EDT 2021. Contains 347654 sequences. (Running on oeis4.)