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

Author

Amarnath Murthy, Aug 28 2003

Keywords

• nonn

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

Examples

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

Crossrefs

Cf. A086550.

Extensions

More terms from David Wasserman, Mar 24 2005