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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.
2
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
EXAMPLE
a(6) = 60 as tau(60)/ tau(59) = 12/2 = 6.
CROSSREFS
Cf. A086550.
Sequence in context: A006774 A361865 A356857 * A254215 A007214 A189736
KEYWORD
nonn
AUTHOR
Amarnath Murthy, Aug 28 2003
EXTENSIONS
More terms from David Wasserman, Mar 24 2005
STATUS
approved