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 A124739 #9 Oct 11 2019 10:59:38
%S A124739 1,1,1,4,1,6,9,13,8,20,13,24,29,25,32,64,37,54,61,61,55,110,73,91,111,
%T A124739 108,114,168,91,120,225,170,153,199,144,216,305,221,175,320,211,252,
%U A124739 397,261,249,506,337,342,423,351,403,624,433,410,483,431,493,812,421,480
%N A124739 a(n) = sum of those positive integers which are coprime to both n and n+1 and which are <= n.
%e A124739 The positive integers which are coprime to 8 and which are <= 8 are 1,3,5,7. The integers which are coprime to 9 and which are <= 9 are 1, The integers in both these sequences (1,5,7) are added get a(8) = 13.
%t A124739 f[n_] := Plus @@ Select[Range[n], GCD[n, # ] == GCD[n + 1, # ] == 1 &];Table[f[n], {n, 60}] (* _Ray Chandler_, Nov 10 2006 *)
%Y A124739 Cf. A057475, A124738, A124740, A124741.
%K A124739 nonn
%O A124739 1,4
%A A124739 _Leroy Quet_, Nov 06 2006
%E A124739 Extended by _Ray Chandler_, Nov 10 2006