a(n) = (2*n+5)*(2*n+1).

Terms

a(0) =5a(1) =21a(2) =45a(3) =77a(4) =117a(5) =165a(6) =221a(7) =285a(8) =357a(9) =437a(10) =525a(11) =621a(12) =725a(13) =837a(14) =957a(15) =1085a(16) =1221a(17) =1365a(18) =1517a(19) =1677a(20) =1845a(21) =2021a(22) =2205a(23) =2397a(24) =2597a(25) =2805a(26) =3021a(27) =3245a(28) =3477a(29) =3717