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 A374213 #8 Jun 30 2024 22:13:14 %S A374213 0,0,0,1,0,1,1,1,0,1,0,1,0,0,0,1,1,1,0,0,0,1,0,1,0,3,0,1,0,1,0,0,0,1, %T A374213 1,1,0,0,3,1,0,1,0,1,0,1,0,1,0,0,0,1,3,2,4,0,0,1,0,1,0,1,1,2,0,1,0,0, %U A374213 0,1,1,1,0,0,0,2,0,1,0,3,0,1,0,1,0,0,1,1,1,2,0,0,0,1,0,1,0,1,0,1,0,1,1,0,0,1,4 %N A374213 The 3-adic valuation of A328768(n), where A328768 is the first primorial based variant of the arithmetic derivative. %H A374213 Antti Karttunen, <a href="/A374213/b374213.txt">Table of n, a(n) for n = 2..100000</a> %F A374213 a(n) = A007949(A328768(n)). %o A374213 (PARI) %o A374213 A002110(n) = prod(i=1,n,prime(i)); %o A374213 A328768(n) = if(n<=1, 0, my(f=factor(n)); n*sum(i=1, #f~, f[i, 2]*A002110(primepi(f[i,1])-1)/f[i, 1])); %o A374213 A374213(n) = valuation(A328768(n), 3); %Y A374213 Cf. A007949, A328768, A373991, A373992 (after its two initial terms, gives the indices of nonzero terms in this sequence). %Y A374213 Cf. also A374133, A374212. %K A374213 nonn %O A374213 2,26 %A A374213 _Antti Karttunen_, Jun 30 2024