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 A078558 #14 Mar 27 2020 06:32:19 %S A078558 1,2,8,48,96,1152,9216,1658880,3317760,92897280,2786918400, %T A078558 100329062400,802632499200,370816214630400,741632429260800, %U A078558 2966529717043200,29665297170432000,355983566045184000 %N A078558 GCD of sigma(p#) and phi(p#) where p# = A002110(n) is the product of the first n primes. %H A078558 Harvey P. Dale, <a href="/A078558/b078558.txt">Table of n, a(n) for n = 1..400</a> %F A078558 a(n) = gcd(A000203(A002110(n)), A000005(A002110(n))) = gcd(A005867(n), A054640(n)). %e A078558 m=2,3,30,210 primorials are balanced numbers so these GCD() equals phi(): a(n)=1,2,8,48 (see A005867). %t A078558 GCD[DivisorSigma[1,#],EulerPhi[#]]&/@FoldList[Times,Prime[Range[20]]] (* _Harvey P. Dale_, Feb 28 2016 *) %o A078558 (PARI) a(n)=gcd(prod(i=1,n,prime(i)-1),prod(i=1,n,prime(i)+1)) \\ _Charles R Greathouse IV_, Dec 09 2013 %Y A078558 Cf. A000203, A002110, A000005, A005867, A054640, A020492. %K A078558 nonn %O A078558 1,2 %A A078558 _Labos Elemer_, Dec 06 2002