A068629 a(1) = 1. a(n) = n*a(n-1) if gcd(n,a(n-1)) = 1, a(n-1)/n if n divides a(n-1), otherwise a(n) = a(n-1).

1, 2, 6, 6, 30, 5, 35, 280, 2520, 252, 2772, 231, 3003, 3003, 3003, 48048, 816816, 816816, 15519504, 15519504, 739024, 33592, 772616, 772616, 19315400, 742900, 20058300, 20058300, 581690700, 19389690, 601080390, 601080390

Offset: 1

Author

Amarnath Murthy, Feb 26 2002

Keywords

• easy
• nonn

Comments

The sequence can also be obtained by taking a(1) = 1 and then multiplying the previous term by n if n is coprime to the previous term a(n-1), dividing the previous term by n if n divides the previous term a(n-1), taking a(n) = a(n-1) if n is unrelated to a(n-1). - Amarnath Murthy, Oct 30 2002 (corrected by Franklin T. Adams-Watters, Dec 13 2006)

Links

• Ivan Neretin, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A034386, A068626, A068627, A068628.

Programs

Mathematica

a = {1}; Do[AppendTo[a, If[GCD[a[[-1]], n] == 1, a[[-1]]*n, If[Divisible[a[[-1]], n], a[[-1]]/n, a[[-1]]]]], {n, 2, 32}]; a (* Ivan Neretin, May 21 2015 *)

PARI

print1(k=1); for(n=2,99, if(gcd(k,n)==1, k*=n, if(k%n==0, k/=n)); print1(", "k)) \\ Charles R Greathouse IV, May 21 2015

Extensions

a(26)-a(32) corrected by Ivan Neretin, May 21 2015