A367577 - OEIS

%I #5 Nov 24 2023 09:00:38

%S 252,1,2,-1,24,5,48,-1,-1,-1,450,-1,12,15,4,-1,1512,-1,18,-1,-1,45,

%T 8118,-1,-1,-1,-1,-1,840,-1,30,-1,10,-1,6,-1,1368,189,-1,-1,1680,-1,

%U 42,-1,-1,231,2208,-1,-1,-1,152,-1,6942,-1,-1,-1,-1,-1,27318,-1,60

%N a(n) is the first k such that A367566(k) = n, or -1 if no such k exists.

%C a(n) = -1 iff n is nonsquarefree or is divisible by some term in A367576.

%e a(1) = 252 because 1 first appears as a term in A367566 at A367566(252).

%e a(4) = -1 because 4 = 2^2 is nonsquarefree so it never appears in A367566.

%e a(10) = -1 because 10 is a term in A367576.

%e a(42) = -1 because 21 divides 42, and 21 is a term in A367576.

%Y Cf. A367566, A367576.

%K sign

%O 1,1

%A _Jon E. Schoenfield_, Nov 24 2023