A138113 a(n) is the smallest number with same number of divisors as n*a(n-1).

1, 2, 6, 24, 120, 720, 5040, 27720, 166320, 1441440, 7207200, 73513440, 367567200, 4655851200, 64250746560, 1028011944960, 5140059724800, 32607253879200, 260858031033600, 4620913692595200, 97039187544499200, 897612484786617600, 9873737332652793600

Offset: 1

Author

J. Lowell, May 04 2008

Keywords

• nonn

Examples

			For n=8, n*a(n-1) = 8*5040 = 40320 has 96 divisors, but the smallest number with 96 divisors is 27720, so a(8)=27720.
		

Crossrefs

Cf. A019505 (2*a(n-1)).

Cf. A140635.

Programs

PARI

A138113(n)={ local(an1,t) ; if(n<=2, return(n) ) ; an1 = A138113(n-1) ; t=length(divisors(n*an1)) ; return(A005179(t)) ; } {for (n=1,40, print1(A138113(n)", ") ; ) } \\ R. J. Mathar, Mar 20 2010

Formula

a(n) = A140635(n*a(n-1)). - J. Lowell, May 20 2008

Extensions

More terms from R. J. Mathar, Mar 20 2010

a(23) from Jon E. Schoenfield, Mar 17 2022