A271531 - OEIS

%I #18 Mar 13 2018 06:45:25

%S 1,1,2,1,12,1,30,3,28,9,24,5,132,3,26,7,420,1,360,3,4,5,1680,253,84,

%T 15,440,117,1020,7,42,15,28,725,2376,1,47880,3,2960,1,29640,155,120,

%U 21,476,11781,11040,1,2640,3,1288,5,300,13,144,285,2860,7,4200,1

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

%H Peter Kagey, <a href="/A271531/b271531.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): lcm(1, 2) = 2;

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

%e a(5) = 12, because 5 == k (mod k) for 0 < k < 5: lcm(1, 2, 3, 4) = 12.

%o (PARI) lista(nn) = {va = vector(nn); va[1] = 1; print1(va[1], ", "); for (n=2, nn, new = 1; for (k=1, n-1, if (Mod(va[k], k) == Mod(n, k), new = lcm(new, k););); va[n] = new; print1(va[n], ", "););} \\ _Michel Marcus_, Mar 13 2018

%K nonn

%O 1,3

%A _Peter Kagey_, Apr 09 2016