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URL: https://oeis.org/A339090

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A339090
GCD of friendly pairs.
0
2, 10, 40, 8, 6, 6, 22, 26, 34, 2, 4, 38, 120, 46, 24, 50, 58, 9, 62, 72, 74, 82, 30, 86, 94, 280, 106, 12, 6, 110, 42, 18, 6, 118, 122, 360, 130, 134, 142, 72, 146, 440, 158, 166, 170, 88, 10, 20, 178, 66, 520, 190, 194, 202, 206, 104, 66, 214, 218, 226, 230
OFFSET
1,1
COMMENTS
The first 10000 friendly pairs (copied from the b-files of A050972 and A050973) all have either 2 or 3 (or both) as a common divisor and hence their GCD is divisible by 2 or 3. However this does not hold for all friendly pairs. GCD(3472, 544635) = 7. These two numbers belong to the club where sigma(x)/x = 16/7 (also 42 belongs to this club).
FORMULA
a(n) = gcd(A050972(n), A050973(n)).
EXAMPLE
The first friendly pair is (6, 28) and therefore a(1) = gcd(6, 28) = 2.
CROSSREFS
Sequence in context: A151312 A253590 A184433 * A244376 A009338 A261473
KEYWORD
nonn,easy
AUTHOR
Ruediger Jehn, Nov 23 2020
STATUS
approved