A169902 Earliest sequence such that xy | a(x+y) and (x+y) | a(xy) for all x >= 1, y >= 1.

2, 3, 4, 60, 12, 2520, 120, 5040, 2520, 277200, 2520, 4324320, 27720, 5045040, 10810800, 49008960, 720720, 4190266080, 12252240, 4655851200, 4888643760, 117793035360, 232792560, 642507465600, 26771144400, 2088149263200

Offset

1,1

Links

Charlie Neder, Table of n, a(n) for n = 1..1000

Prog

(Python)
from math import gcd
for n in range(1, 1001):
  a_n = 1
  res = []
  for addend in range(1, n//2+1): res.append(addend*(n - addend))
  for dividend in range(1, n+1):
    if not n%dividend: res.append(dividend + n//dividend)
    if dividend*dividend >= n: break
  for i in res: a_n *= i // gcd(a_n, i)
  print(n, a_n)
# Charlie Neder, Oct 09 2018

Crossrefs

Sequence in context: A282034 A096782 A098811 * A004855 A097930 A012322

Adjacent sequences: A169899 A169900 A169901 * A169903 A169904 A169905

Keyword

nonn,nice

Author

Andrew Weimholt, Jul 05 2010

Status

approved