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.

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

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: A006774 A361865 A356857 * 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