A271531 a(1) = 1; thereafter a(n) is the LCM of all 0 < m < n for which n == a(m) (mod m).

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, 15, 440, 117, 1020, 7, 42, 15, 28, 725, 2376, 1, 47880, 3, 2960, 1, 29640, 155, 120, 21, 476, 11781, 11040, 1, 2640, 3, 1288, 5, 300, 13, 144, 285, 2860, 7, 4200, 1

Offset: 1

Author

Peter Kagey, Apr 09 2016

Keywords

• nonn

Examples

			a(1) = 1 by definition.
a(2) = 1, because 2 == a(1) (mod 1);
a(3) = 2, because 3 == a(1) (mod 1), and 3 == a(2) (mod 2): lcm(1, 2) = 2;
a(4) = 1, because 4 == a(1) (mod 1);
a(5) = 12, because 5 == k (mod k) for 0 < k < 5: lcm(1, 2, 3, 4) = 12.
		

Links

• Peter Kagey, Table of n, a(n) for n = 1..10000

Programs

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