a(n) = 18*2^n + 10.

Terms

a(0) =28a(1) =46a(2) =82a(3) =154a(4) =298a(5) =586a(6) =1162a(7) =2314a(8) =4618a(9) =9226a(10) =18442a(11) =36874a(12) =73738a(13) =147466a(14) =294922a(15) =589834a(16) =1179658a(17) =2359306a(18) =4718602a(19) =9437194a(20) =18874378a(21) =37748746a(22) =75497482a(23) =150994954a(24) =301989898a(25) =603979786a(26) =1207959562a(27) =2415919114a(28) =4831838218a(29) =9663676426