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A169902 Earliest sequence such that xy | a(x+y) and (x+y) | a(xy) for all x >= 1, y >= 1. 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 (list; graph; refs; listen; history; text; internal format)
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

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Last modified November 16 03:41 EST 2018. Contains 317252 sequences. (Running on oeis4.)