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 A379473 #9 Dec 27 2024 18:08:53 %S A379473 1,3,1,1,3,3,1,3,1,9,3,1,1,3,3,1,9,3,1,3,1,9,3,3,1,3,1,1,3,9,1,9,3,27, %T A379473 3,1,1,3,1,9,3,3,1,3,3,9,3,1,3,3,9,1,27,3,9,3,1,9,3,3,1,3,1,1,3,9,1,9, %U A379473 3,9,9,3,1,3,1,1,3,3,1,3,1,9,3,1,27,3,3,9,9,9,1,3,1,9,3,9,1,9,3,1,3,27,1,3,3 %N A379473 a(n) is the highest power of 3 dividing the sum of divisors of n. %H A379473 Antti Karttunen, <a href="/A379473/b379473.txt">Table of n, a(n) for n = 1..20000</a> %H A379473 <a href="/index/Si#SIGMAN">Index entries for sequences related to sigma(n)</a>. %F A379473 Multiplicative with a(p^e) = A038500((p^(e+1)-1)/(p-1)). %F A379473 a(n) = A038500(A000203(n)). %F A379473 a(n) = A000244(A354100(n)). %t A379473 a[n_] := 3^IntegerExponent[DivisorSigma[1, n], 3]; Array[a, 100] (* _Amiram Eldar_, Dec 27 2024 *) %o A379473 (PARI) A379473(n) = (3^valuation(sigma(n),3)); %Y A379473 Cf. A000203, A000244, A038500, A354100, A379484 [= a(A379481(n))]. %Y A379473 Cf. A329963 (positions of 1's), A087943 (of terms > 1). %Y A379473 Cf. also A082903. %K A379473 nonn,mult %O A379473 1,2 %A A379473 _Antti Karttunen_, Dec 27 2024