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

1,2

Links

Table of n, a(n) for n=1..23.

Formula

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

Example

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.

Prog

(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

Crossrefs

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

Cf. A140635.

Sequence in context: A276841 A364427 A273694 * A045977 A177278 A173847

Adjacent sequences: A138110 A138111 A138112 * A138114 A138115 A138116

Keyword

nonn

Author

J. Lowell, May 04 2008

Extensions

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

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

Status

approved