A169902 - OEIS

%I #13 Oct 11 2018 11:51:48

%S 2,3,4,60,12,2520,120,5040,2520,277200,2520,4324320,27720,5045040,

%T 10810800,49008960,720720,4190266080,12252240,4655851200,4888643760,

%U 117793035360,232792560,642507465600,26771144400,2088149263200

%N Earliest sequence such that xy | a(x+y) and (x+y) | a(xy) for all x >= 1, y >= 1.

%H Charlie Neder, <a href="/A169902/b169902.txt">Table of n, a(n) for n = 1..1000</a>

%o (Python)

%o from math import gcd

%o for n in range(1,1001):

%o ..a_n = 1

%o ..res = []

%o ..for addend in range(1,n//2+1): res.append(addend*(n - addend))

%o ..for dividend in range(1,n+1):

%o ....if not n%dividend: res.append(dividend + n//dividend)

%o ....if dividend*dividend >= n: break

%o ..for i in res: a_n *= i // gcd(a_n,i)

%o ..print(n,a_n)

%o # _Charlie Neder_, Oct 09 2018

%K nonn,nice

%O 1,1

%A _Andrew Weimholt_, Jul 05 2010