A339090 GCD of friendly pairs.

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).

Links

Table of n, a(n) for n=1..61.

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

Cf. A050972, A050973.

Sequence in context: A151312 A253590 A184433 * A244376 A009338 A261473

Adjacent sequences: A339087 A339088 A339089 * A339091 A339092 A339093

Keyword

nonn,easy

Author

Ruediger Jehn, Nov 23 2020

Status

approved