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 A163373 #11 Sep 08 2022 08:45:46 %S A163373 1,1,1,2,1,2,2,4,4,2,2,4,2,4,4,8,2,8,4,4,8,4,4,8,8,4,8,8,4,8,8,12,8,6, %T A163373 8,24,6,8,8,8,4,16,8,8,8,8,8,16,12,16,8,12,6,16,8,16,16,8,8,16,8,16, %U A163373 16,36,8,16,16,12,16,16,8,32,12,12,16,16,16,16,16 %N A163373 a(n) = phi(phi(sigma(n))). %C A163373 a(n) = A000010(A000010(A000203(n))) = A000010(A062401(n)) = A010554(A000203(n)). %H A163373 G. C. Greubel, <a href="/A163373/b163373.txt">Table of n, a(n) for n = 1..1000</a> %F A163373 a(n) = A000010(A000010(A000203(n))) = A000010(A062401(n)) = A010554(A000203(n)). %t A163373 EulerPhi[EulerPhi[DivisorSigma[1, Range[100]]]] (* _G. C. Greubel_, Dec 20 2016 *) %o A163373 (PARI) vector(100, n, eulerphi(eulerphi(sigma(n)))) \\ _G. C. Greubel_, Dec 20 2016 %o A163373 (Magma) [EulerPhi(EulerPhi(SumOfDivisors(n))): n in [1..80]]; // _Vincenzo Librandi_, Dec 20 2016 %Y A163373 Cf. A000010, A000203, A010554, A062401. %K A163373 nonn %O A163373 1,4 %A A163373 _Jaroslav Krizek_, Jul 25 2009