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 A372672 #10 May 10 2024 08:49:16
%S A372672 1,2,2,4,5,4,6,8,6,10,10,8,12,12,10,16,16,12,18,20,12,20,22,16,25,24,
%T A372672 18,24,28,20,30,32,20,32,30,24,36,36,24,40,40,24,42,40,30,44,46,32,42,
%U A372672 50,32,48,52,36,50,48,36,56,58,40,60,60,36,64,60,40,66,64,44,60,70,48,72,72,50,72,60,48
%N A372672 a(n) = phi(10 * n)/4.
%F A372672 G.f.: Sum_{k>=1} mu(10 * k) * x^k / (1 - x^k)^2, where mu() is the Moebius function (A008683).
%F A372672 Multiplicative with a(p^e) = p^e if p = 2 or 5, and (p-1)*p^(e-1) otherwise.
%o A372672 (PARI) a(n) = eulerphi(10*n)/4;
%o A372672 (PARI) my(N=80, x='x+O('x^N)); Vec(sum(k=1, N, moebius(10*k)*x^k/(1-x^k)^2))
%Y A372672 Partial sums gives A372639.
%Y A372672 Column k=10 of A372673.
%Y A372672 Cf. A008683.
%K A372672 nonn,easy
%O A372672 1,2
%A A372672 _Seiichi Manyama_, May 10 2024