A331757(n)/2.

Terms

a(0) =4a(1) =14a(2) =40a(3) =89a(4) =186a(5) =327a(6) =562a(7) =891a(8) =1362a(9) =1957a(10) =2790a(11) =3813a(12) =5176a(13) =6795a(14) =8770a(15) =11105a(16) =14020a(17) =17335a(18) =21380a(19) =25981a(20) =31306a(21) =37247a(22) =44254a(23) =52021a(24) =60956a(25) =70767a(26) =81832a(27) =93971a(28) =107818a(29) =122745