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 A367577 #5 Nov 24 2023 09:00:38 %S A367577 252,1,2,-1,24,5,48,-1,-1,-1,450,-1,12,15,4,-1,1512,-1,18,-1,-1,45, %T A367577 8118,-1,-1,-1,-1,-1,840,-1,30,-1,10,-1,6,-1,1368,189,-1,-1,1680,-1, %U A367577 42,-1,-1,231,2208,-1,-1,-1,152,-1,6942,-1,-1,-1,-1,-1,27318,-1,60 %N A367577 a(n) is the first k such that A367566(k) = n, or -1 if no such k exists. %C A367577 a(n) = -1 iff n is nonsquarefree or is divisible by some term in A367576. %e A367577 a(1) = 252 because 1 first appears as a term in A367566 at A367566(252). %e A367577 a(4) = -1 because 4 = 2^2 is nonsquarefree so it never appears in A367566. %e A367577 a(10) = -1 because 10 is a term in A367576. %e A367577 a(42) = -1 because 21 divides 42, and 21 is a term in A367576. %Y A367577 Cf. A367566, A367576. %K A367577 sign %O A367577 1,1 %A A367577 _Jon E. Schoenfield_, Nov 24 2023