A271530 - OEIS

%I #16 Apr 09 2016 20:29:57

%S 1,1,2,1,24,1,12,3,40,1,480,7,432,15,28,13,24,11,40320,3,1520,9,120,

%T 85,48,21,16,345,1452971520,1,8553600,3,56,5,44544,1,1161216,3,340,

%U 13167,155040,13,130636800,15,4736,1,36167040,1075,66960,63,40480,1,27456

%N a(1) = 1; thereafter a(n) is the product of all 0 < m < n for which n == a(m) (mod m).

%H Peter Kagey, <a href="/A271530/b271530.txt">Table of n, a(n) for n = 1..10000</a>

%e a(1) = 1 by definition.

%e a(2) = 1, because 2 == a(1) (mod 1);

%e a(3) = 2, because 3 == a(1) (mod 1), and 3 == a(2) (mod 2): 1 * 2 = 2;

%e a(4) = 1, because 4 == a(1) (mod 1);

%e a(5) = 24, because 5 == k (mod k) for 0 < k < 5: 1 * 2 * 3 * 4 = 24.

%t a = {1}; Do[AppendTo[a, Times @@ Flatten@ Position[MapIndexed[Mod[n, First@ #2] == Mod[#1, First@ #2] &, a], True]], {n, 2, 53}]; a (* _Michael De Vlieger_, Apr 09 2016 *)

%Y Cf. A269423, A271531.

%K nonn

%O 1,3

%A _Peter Kagey_, Apr 09 2016