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A169902
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Earliest sequence such that xy | a(x+y) and (x+y) | a(xy) for all x >= 1, y >= 1.
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1
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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
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OFFSET
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1,1
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LINKS
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PROG
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(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)
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CROSSREFS
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KEYWORD
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nonn,nice
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AUTHOR
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STATUS
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approved
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