A347303 a(n) = 3^(n-1) - lcm{1..n}.
0, 1, 3, 15, 21, 183, 309, 1347, 4041, 17163, 31329, 149427, 171081, 1233963, 4422609, 13628187, 30794481, 116887923, 154627929, 929468907, 3253991841, 10227560643, 26026830729, 88788949947, 255658392081, 820517465043, 2461552395129, 7545284051787, 20547702892161
Offset: 1