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 A308993 #13 Jul 07 2019 13:09:30 %S A308993 1,1,1,2,1,1,1,2,3,1,1,2,1,1,1,4,1,3,1,2,1,1,1,2,5,1,3,2,1,1,1,2,1,1, %T A308993 1,6,1,1,1,2,1,1,1,2,3,1,1,4,7,5,1,2,1,3,1,2,1,1,1,2,1,1,3,2,1,1,1,2, %U A308993 1,1,1,6,1,1,5,2,1,1,1,4,9,1,1,2,1,1,1 %N A308993 Multiplicative with a(p) = 1 and a(p^e) = p^a(e) for any e > 1 and prime number p. %C A308993 To compute a(n): remove every prime number at leaf position in the prime tower factorization of n (the prime tower factorization of a number is defined in A182318). %H A308993 Rémy Sigrist, <a href="/A308993/b308993.txt">Table of n, a(n) for n = 1..10000</a> %H A308993 Rémy Sigrist, <a href="/A308993/a308993.pdf">Illustration of first terms</a> %F A308993 a(n) = 1 iff n is squarefree. %F A308993 a^k(n) = 1 for any k >= A185102(n) (where a^k denotes the k-th iterate of a). %F A308993 a(n)^2 <= n with equality iff n is the square of some cubefree number (n = A004709(k)^2 for some k > 0). %e A308993 See Links sections. %o A308993 (PARI) a(n) = my (f=factor(n)); prod (i=1, #f~, f[i,1]^if (f[i,2]==1, 0, a(f[i,2]))) %Y A308993 Cf. A004709, A005117, A182318, A185102. %K A308993 nonn,mult %O A308993 1,4 %A A308993 _Rémy Sigrist_, Jul 04 2019