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 A354100 #15 May 18 2023 10:40:39
%S A354100 0,1,0,0,1,1,0,1,0,2,1,0,0,1,1,0,2,1,0,1,0,2,1,1,0,1,0,0,1,2,0,2,1,3,
%T A354100 1,0,0,1,0,2,1,1,0,1,1,2,1,0,1,1,2,0,3,1,2,1,0,2,1,1,0,1,0,0,1,2,0,2,
%U A354100 1,2,2,1,0,1,0,0,1,1,0,1,0,2,1,0,3,1,1,2,2,2,0,1,0,2,1,2,0,2,1,0,1,3,0,1,1
%N A354100 The 3-adic valuation of sigma, sum of divisors function.
%H A354100 Antti Karttunen, <a href="/A354100/b354100.txt">Table of n, a(n) for n = 1..65537</a>
%H A354100 <a href="/index/Si#SIGMAN">Index entries for sequences related to sigma(n)</a>.
%F A354100 a(n) = A007949(A000203(n)).
%F A354100 Additive with a(p^e) = A007949((p^(e+1)-1)/(p-1)).
%t A354100 a[n_] := IntegerExponent[DivisorSigma[1, n], 3]; Array[a, 100] (* _Amiram Eldar_, May 18 2023 *)
%o A354100 (PARI) A354100(n) = valuation(sigma(n),3);
%o A354100 (PARI) A354100(n) = { my(f=factor(n)); sum(k=1,#f~,valuation(((f[k,1]^(f[k,2]+1))-1)/(f[k,1]-1), 3)); }; \\ Demonstrates the additivity
%Y A354100 Cf. A000203, A007949, A074941.
%Y A354100 Cf. A329963 (positions of zeros), A087943 (of terms > 0).
%Y A354100 Cf. also A336937, A354099.
%K A354100 nonn
%O A354100 1,10
%A A354100 _Antti Karttunen_, May 17 2022