OFFSET
1,2
COMMENTS
Also a(n) = lcm(1,...,(2n+2))/12. - Paul Barry, Jun 09 2006. Proof that this is the same sequence, from Martin Fuller, May 06 2007: k, k+1, 2k+1 are coprime so their lcm is the same as their product. Hence a(n) = lcm{k, k+1, 2k+1 | k=1..n}/6. {k, k+1, 2k+1 | k=1..n} = {1..2n+2 excluding even numbers >n+1}. Adding the higher even numbers to the set doubles the LCM. Hence lcm{k, k+1, 2k+1 | k=1..n}/6 = lcm{1..2n+2}/12.
LINKS
Reinhard Zumkeller, Table of n, a(n) for n = 1..1000
EXAMPLE
a(4) = lcm(1, 5, 14, 30) = 210.
MATHEMATICA
Table[LCM@@Range[2n+2]/12, {n, 30}] (* Harvey P. Dale, Apr 25 2011 *)
PROG
(Haskell)
a051538 n = a051538_list !! (n-1)
a051538_list = scanl1 lcm $ tail a000330_list
-- Reinhard Zumkeller, Mar 12 2014
(Magma) [Lcm([1..2*n+2])/12: n in [1..30]]; // G. C. Greubel, May 03 2023
(SageMath)
def A051538(n):
return lcm(range(1, 2*n+3))/12
[A051538(n) for n in range(1, 31)] # G. C. Greubel, May 03 2023
CROSSREFS
KEYWORD
easy,nice,nonn
AUTHOR
EXTENSIONS
Corrected by James A. Sellers
Edited by N. J. A. Sloane, May 06 2007
STATUS
approved