A076965 a(1) = 2; thereafter a(n) is the smallest number coprime to a(n-1) and having a(n-1) divisors.

2, 3, 4, 15, 784, 526121578125

Offset

1,1

Comments

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]

Links

Nathaniel Johnston, Table of n,a(n) for n=1..7

XKCD Forums, Extending A076965 [From Nathaniel Johnston, Nov 28 2008]

Example

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

Crossrefs

Cf. A076964.

Sequence in context: A281586 A365739 A217714 * A370694 A375280 A113232

Adjacent sequences: A076962 A076963 A076964 * A076966 A076967 A076968

Keyword

nonn

Author

Amarnath Murthy, Oct 21 2002

Extensions

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

Status

approved