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A086551 a(n) = smallest k such that tau(k)= n*tau(k-1) where tau(k) = number of divisors of k, or 0 if no such number exists. 1
3, 2, 12, 24, 48, 60, 192, 168, 180, 240, 5120, 360, 20480, 2112, 720, 840, 983040, 1260, 786432, 3024, 2880, 15360, 62914560, 3360, 22032, 266240, 6300, 6720, 13690208256, 5040, 22548578304, 7560, 156672, 6881280, 25920, 10080 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Conjectures: (1) No term is zero. (2) a(n)-1 is a prime.

17 is the first n such that a(n)-1 is composite. a(17) = 2^16*3*5 and a(17)-1 is a product of two primes. - David Wasserman, Mar 24 2005

LINKS

Table of n, a(n) for n=1..36.

EXAMPLE

a(6) = 60 as tau(60)/ tau(59) = 12/2 = 6.

CROSSREFS

Cf. A086550.

Sequence in context: A113205 A136657 A006774 * A254215 A007214 A189736

Adjacent sequences:  A086548 A086549 A086550 * A086552 A086553 A086554

KEYWORD

nonn

AUTHOR

Amarnath Murthy, Aug 28 2003

EXTENSIONS

More terms from David Wasserman, Mar 24 2005

STATUS

approved

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Last modified September 15 14:53 EDT 2019. Contains 327078 sequences. (Running on oeis4.)