This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A339090 #23 Dec 23 2020 20:36:20 %S A339090 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, %T A339090 280,106,12,6,110,42,18,6,118,122,360,130,134,142,72,146,440,158,166, %U A339090 170,88,10,20,178,66,520,190,194,202,206,104,66,214,218,226,230 %N A339090 GCD of friendly pairs. %C A339090 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). %F A339090 a(n) = gcd(A050972(n), A050973(n)). %e A339090 The first friendly pair is (6, 28) and therefore a(1) = gcd(6, 28) = 2. %Y A339090 Cf. A050972, A050973. %K A339090 nonn,easy %O A339090 1,1 %A A339090 _Ruediger Jehn_, Nov 23 2020