a(n) is the total semiperimeter over all Motzkin polyominoes of length n.

Terms

a(0) =0a(1) =2a(2) =4a(3) =11a(4) =29a(5) =80a(6) =222a(7) =624a(8) =1766a(9) =5030a(10) =14396a(11) =41371a(12) =119297a(13) =345008a(14) =1000274a(15) =2906427a(16) =8461269a(17) =24674718a(18) =72065892a(19) =210766089a(20) =617173791a(21) =1809257448a(22) =5309289426a(23) =15594735954a(24) =45845032212a(25) =134880781266a(26) =397123496252