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 A328578 #28 Oct 30 2019 08:31:12
%S A328578 2,1,3,1,4,1,3,1,4,1,5,1,2,1,5,1,4,1,3,1,6,1,6,1,2,1,6,1,7,1,2,1,4,1,
%T A328578 3,1,3,1,5,1,6,1,2,1,6,1,6,1,3,1,7,1,7,1,2,1,7,1,5,1,2,1,5,1,4,1,3,1,
%U A328578 6,1,6,1,2,1,7,1,7,1,3,1,7,1,8,1,2,1,6,1,8,1,2,1,6,1,7,1,3,1,7,1,7,1,2,1,7,1
%N A328578 Index of the least prime not dividing A276086(A276086(n)): a(n) = A257993(A276087(n)).
%C A328578 Index of the least significant zero digit in the primorial base expansion of A276086(n), when the rightmost digit is in the position 1.
%C A328578 The scatter plot shows both regular looking as well as more chaotic regions. This can be more clearly seen in related A328579. See also A328839.
%H A328578 Antti Karttunen, <a href="/A328578/b328578.txt">Table of n, a(n) for n = 0..32768</a>
%H A328578 Rémy Sigrist, <a href="/A328578/a328578.png">Colored logarithmic scatterplot of the ordinal transform of the sequence for n = 0..510510</a>
%H A328578 Rémy Sigrist, <a href="/A328578/a328578_1.png">Density plot of the sequence for n = 0..510510</a>
%H A328578 <a href="/index/Pri#primorialbase">Index entries for sequences related to primorial base</a>
%F A328578 a(n) = A328570(A276086(n)) = A257993(A276087(n)) = A055396(A328403(n)).
%F A328578 a(n) = A000720(A328579(n)).
%F A328578 a(n) = A257993(n) + A328590(n).
%F A328578 a(n) = A055396(A328763(n)).
%F A328578 For all n >= 0, a(A328761(n)) = n.
%o A328578 (PARI)
%o A328578 A276086(n) = { my(m=1, p=2); while(n, m *= (p^(n%p)); n = n\p; p = nextprime(1+p)); (m); };
%o A328578 A328570(n) = { my(i=1, p=2); while(n && (n%p), i++; n = n\p; p = nextprime(1+p)); (i); };
%o A328578 A328578(n) = A328570(A276086(n));
%o A328578 (PARI)
%o A328578 A257993(n) = { for(i=1,oo,if(n%prime(i),return(i))); }
%o A328578 A328578(n) = A257993(A276086(A276086(n)));
%Y A328578 Cf. A000720, A055396, A276086, A276087, A328403, A328570, A328579 (the corresponding prime), A328590, A328763, A328766, A328839.
%Y A328578 Cf. A328585 (where equal with A257993), A328587 (less than), A328588 (greater than).
%Y A328578 Cf. A328761 (the first occurrence of each n).
%Y A328578 Cf. also array A328631 and its rows A005408, A328632, A328633, A328634, A328635, A328636 (positions of terms 1 .. 6 in this sequence).
%K A328578 nonn,look
%O A328578 0,1
%A A328578 _Antti Karttunen_, Oct 20 2019