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 A058515 #25 May 07 2025 03:04:56 %S A058515 1,1,2,2,2,2,2,2,2,2,2,4,6,2,8,8,2,6,2,4,2,2,2,4,4,6,6,4,4,2,2,4,4,8, %T A058515 12,12,18,6,8,8,4,6,2,4,2,2,2,2,2,4,8,4,2,2,8,12,4,2,2,4,30,6,4,16,4, %U A058515 2,2,4,4,2,2,24,36,4,4,12,12,6,2,2,2,2,2,8,2,14,8,8,8,24,4,4,2,2,8,32,6 %N A058515 GCD of totients of consecutive integers. %H A058515 Antti Karttunen, <a href="/A058515/b058515.txt">Table of n, a(n) for n = 1..10000</a> %F A058515 a(n) = gcd(phi(n+1), phi(n)), where phi = A000010. %F A058515 a(n) = A083542(n)/A066813(n). - _Amiram Eldar_, May 07 2025 %e A058515 For n = 61, gcd(phi(62), phi(61)) = gcd(30, 60) = 30, so a(61) = 30. %t A058515 Map[GCD @@ # &, Partition[EulerPhi@ Range@ 98, 2, 1]] (* _Michael De Vlieger_, Aug 22 2017 *) %o A058515 (PARI) a(n) = gcd(eulerphi(n), eulerphi(n+1)); \\ _Michel Marcus_, Dec 10 2013 %Y A058515 Cf. A000010, A049586, A060778, A066813, A083542. %K A058515 nonn,easy %O A058515 1,3 %A A058515 _Labos Elemer_, Dec 21 2000 %E A058515 Offset corrected to 1 by _Michel Marcus_, Dec 10 2013