This Number Sequence is Driving me MAD!

[recon]

1,2,4,__,10,___,16,18

I saw this problem in a kid's math textbook, and I still can't figure out what the answer is supposed to be. I can't see the logic. Pls. lend me your thoughts on this.

[gazzo]

Primes minus one.

1, 2, 4, 6, 10, 12, 16 ,18, ...

[recon]

thanks a lot gazzo!!! I owe you one.