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Greatest common divisor of largest square dividing n! and squarefree part of n!.
7

%I #19 Aug 13 2024 21:01:33

%S 1,1,1,2,2,1,1,2,2,1,1,3,3,6,10,10,10,5,5,1,21,42,42,7,7,14,42,6,6,5,

%T 5,10,330,165,231,231,231,462,2002,5005,5005,4290,4290,390,78,39,39,

%U 13,13,26,1326,102,102,17,935,13090,746130,373065,373065,24871,24871

%N Greatest common divisor of largest square dividing n! and squarefree part of n!.

%H Michael De Vlieger, <a href="/A055230/b055230.txt">Table of n, a(n) for n = 1..5000</a>

%F a(n) = GCD(A008833(n!), A007913(n!)) = GCD(A055071(n), A055204(n)).

%e a(5) = 2 because 5! = 120; largest square divisor is 4, squarefree part is 30; GCD(4, 30) = 2.

%e a(7) = 1 because 7! = 5040; the largest square divisor is 144 and the squarefree part is 35 and these are coprime.

%t Table[GCD[Times @@ Flatten@ Map[Table[#1, 2 Floor[#2/2]] & @@ # &, #], Times @@ Flatten@ Map[Table[#1, Floor[Mod[#2, 2]]] & @@ # &, #]] &@ FactorInteger[n!], {n, 61}] (* _Michael De Vlieger_, Jul 26 2016 *)

%o (PARI) a(n) = my(fn=n!, cn=core(fn)); gcd(cn, fn/cn); \\ _Michel Marcus_, Dec 10 2013

%Y Cf. A008833, A007913, A000188, A000720.

%K nonn

%O 1,4

%A _Labos Elemer_, Jun 21 2000