a(n) = floor( (2/(exp(1) - 2))^n ) for n >= 2, a(1) = 1.

Terms

a(0) =1a(1) =7a(2) =21a(3) =60a(4) =167a(5) =466a(6) =1297a(7) =3613a(8) =10060a(9) =28012a(10) =77998a(11) =217180a(12) =604723a(13) =1683804a(14) =4688422a(15) =13054548a(16) =36349377a(17) =101212019a(18) =281817012a(19) =784697597a(20) =2184929553a(21) =6083766752a(22) =16939776315a(23) =47167492325a(24) =131334221349a(25) =365689945495