A087192 a(n) = ceiling[a(n-1)*4/3] with a(1) = 1.

1, 2, 3, 4, 6, 8, 11, 15, 20, 27, 36, 48, 64, 86, 115, 154, 206, 275, 367, 490, 654, 872, 1163, 1551, 2068, 2758, 3678, 4904, 6539, 8719, 11626, 15502, 20670, 27560, 36747, 48996, 65328, 87104, 116139, 154852, 206470, 275294, 367059, 489412, 652550