A076965 - OEIS

%I #6 Dec 05 2013 19:55:47

%S 2,3,4,15,784,526121578125

%N a(1) = 2; thereafter a(n) is the smallest number coprime to a(n-1) and having a(n-1) divisors.

%C a(7) = 2^18 * 7^16 * 23^12 * 29^10 * 31^4 * 37^4 * 41^4 * 43^4 * 47^4 * 53^4 * 59^2 * 61^2 * 67^2 * 71^2 * 73^2 * 79^2, which has 111 digits [From _Nathaniel Johnston_, Nov 28 2008]

%H Nathaniel Johnston, <a href="/A076965/b076965.txt">Table of n,a(n) for n=1..7</a>

%H XKCD Forums, <a href="http://forums.xkcd.com/viewtopic.php?f=17&amp;t=30951&amp;p=1020417">Extending A076965</a> [From _Nathaniel Johnston_, Nov 28 2008]

%e a(4) = 15, a(5) = 784 = 2^4*7^2, tau(784) =5*3 = 15 with (784,15) = 1

%Y Cf. A076964.

%K nonn

%O 1,1

%A _Amarnath Murthy_, Oct 21 2002

%E Added 526121578125 based on its prime factorization of 3^6 * 5^6 * 11 * 13 * 17 * 19, it is the smallest possible number such that gcd(n,784)=1 and d(n)=784. - Kevin Sullivan (kasull88(AT)gmail.com), Nov 24 2008