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 A166641 #18 Feb 05 2025 07:50:29
%S A166641 1,10,20,100,40,200,60,1000,400,400,100,2000,120,600,800,10000,160,
%T A166641 4000,180,4000,1200,1000,220,20000,1600,1200,8000,6000,280,8000,300,
%U A166641 100000,2000,1600,2400,40000,360,1800,2400,40000,400,12000,420,10000,16000
%N A166641 Totally multiplicative sequence with a(p) = 10*(p-1) for prime p.
%H A166641 G. C. Greubel, <a href="/A166641/b166641.txt">Table of n, a(n) for n = 1..10000</a>
%F A166641 Multiplicative with a(p^e) = (10*(p-1))^e. If n = Product p(k)^e(k) then a(n) = Product (10*(p(k)-1))^e(k).
%F A166641 a(n) = A165831(n) * A003958(n) = 10^bigomega(n) * A003958(n) = 10^A001222(n) * A003958(n).
%t A166641 DirichletInverse[f_][1] = 1/f[1]; DirichletInverse[f_][n_] :=
%t A166641 DirichletInverse[f][n] = -1/f[1]*Sum[f[n/d]*DirichletInverse[f][d], {d, Most[Divisors[n]]}]; muphi[n_] := MoebiusMu[n]*EulerPhi[n]; a[m_] := DirichletInverse[muphi][m]; Table[a[m]*10^(PrimeOmega[m]), {m, 1, 100}] (* _G. C. Greubel_, May 20 2016 *)
%t A166641 f[p_, e_] := (10*(p-1))^e; a[1] = 1; a[n_] := Times @@ f @@@ FactorInteger[n]; Array[a, 100] (* _Amiram Eldar_, Oct 17 2023 *)
%o A166641 (PARI) a(n) = {my(f = factor(n)); for (k=1, #f~, f[k,1] = 10*(f[k,1]-1)); factorback(f);} \\ _Michel Marcus_, May 21 2016
%Y A166641 Cf. A001222, A003958, A165831.
%K A166641 nonn,easy,mult
%O A166641 1,2
%A A166641 _Jaroslav Krizek_, Oct 18 2009