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 A351563 #14 Apr 02 2022 10:26:11 %S A351563 0,0,0,0,0,1,0,0,0,1,0,1,0,1,1,0,0,2,0,1,1,1,0,1,0,1,0,1,0,1,0,0,1,1, %T A351563 1,2,0,1,1,1,0,1,0,1,1,1,0,1,0,2,1,1,0,3,1,1,1,1,0,1,0,1,1,0,1,1,0,1, %U A351563 1,1,0,2,0,1,2,1,1,1,0,1,0,1,0,1,1,1,1,1,0,2,1,1,1,1,1,1,0,2,1,2,0,1,0,1,1,1,0,3 %N A351563 a(n) is the exponent of the second smallest prime factor of n, or 0 if n is a power of a prime. %H A351563 Antti Karttunen, <a href="/A351563/b351563.txt">Table of n, a(n) for n = 1..65537</a> %F A351563 a(n) = A067029(A028234(n)). %e A351563 For n = 4 = 2^2 there is no second smallest prime factor as 4 is a power of prime, therefore a(4) = 0. %e A351563 For n = 18 = 2^1 * 3^2, the exponent of the second smallest prime factor (3) is 2, therefore a(18) = 2. %t A351563 Array[If[Length[#] < 2, 0, #[[2, -1]]] &@ FactorInteger[#] &, 108] (* _Michael De Vlieger_, Apr 01 2022 *) %o A351563 (PARI) A351563(n) = if(1>=omega(n), 0, (factor(n))[2,2]); %Y A351563 Cf. A000961 (positions of zeros), A001221, A028234, A067029. %Y A351563 Cf. also A119288, A351567. %K A351563 nonn %O A351563 1,18 %A A351563 _Antti Karttunen_, Apr 01 2022