a(n) = (8*n+3)*(8*n+7).

Terms

a(0) =21a(1) =165a(2) =437a(3) =837a(4) =1365a(5) =2021a(6) =2805a(7) =3717a(8) =4757a(9) =5925a(10) =7221a(11) =8645a(12) =10197a(13) =11877a(14) =13685a(15) =15621a(16) =17685a(17) =19877a(18) =22197a(19) =24645a(20) =27221a(21) =29925a(22) =32757a(23) =35717a(24) =38805a(25) =42021a(26) =45365a(27) =48837a(28) =52437a(29) =56165