|
|
A048803
|
|
a(0) = 1, a(1) = 1; for n > 1, a(n) = lcm( 1, 2, ..., n, a(1)*a(n-1), a(2)*a(n-2), ..., a(n-1)*a(1) ).
|
|
17
|
|
|
1, 1, 2, 6, 12, 60, 360, 2520, 5040, 15120, 151200, 1663200, 9979200, 129729600, 1816214400, 27243216000, 54486432000, 926269344000, 5557616064000, 105594705216000, 1055947052160000, 22174888095360000, 487847538097920000
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
0,3
|
|
COMMENTS
|
Squarefree factorials: a(1) = 1, a(n+1) = a(n)* largest squarefree divisor of (n+1). - Amarnath Murthy, Nov 28 2004
a(n) is the product of the lcm of the set of prime factors of k over the range k = 1..n. - Peter Luschny, Jun 10 2011
|
|
REFERENCES
|
Paul-Jean Cahen and Jean-Luc Chabert, Integer-valued Polynomials, AMS, Providence, RI, 1997. Math. Rev. 98a:13002. See p. 246.
|
|
LINKS
|
|
|
FORMULA
|
a(n) = Product_{p prime} p^floor(n/p). See Farhi link p. 16. - Michel Marcus, Oct 18 2018
For n >=1, a(n) = lcm(1^floor(n/1),2^floor(n/2),...,n^floor(n/n)). - Robert FERREOL, Aug 05 2021
|
|
MAPLE
|
a := n -> mul(NumberTheory:-Radical(i), i=1..n): # Peter Luschny, Mar 14 2022
|
|
MATHEMATICA
|
a[0] = 1; a[n_] := a[n] = a[n-1] First @ Select[Reverse @ Divisors[n], SquareFreeQ, 1]; Array[a, 22, 0] (* Jean-François Alcover, May 04 2011 *)
|
|
PROG
|
(PARI) a(n)=local(f); f=n>=0; if(n>1, forprime(p=2, n, f*=p^(n\p))); f
(Haskell)
a048803 n = a048803_list !! n
a048803_list = scanl (*) 1 a007947_list
(SageMath)
from functools import cache
@cache
def a_rec(n):
if n == 0: return 1
return radical(n) * a_rec(n - 1)
print([a_rec(n) for n in range(23)]) # Peter Luschny, Dec 12 2023
|
|
CROSSREFS
|
|
|
KEYWORD
|
nonn,nice
|
|
AUTHOR
|
|
|
EXTENSIONS
|
|
|
STATUS
|
approved
|
|
|
|