a(n) = binomial(n+1,2)*7^2.

Terms

a(0) =0a(1) =49a(2) =147a(3) =294a(4) =490a(5) =735a(6) =1029a(7) =1372a(8) =1764a(9) =2205a(10) =2695a(11) =3234a(12) =3822a(13) =4459a(14) =5145a(15) =5880a(16) =6664a(17) =7497a(18) =8379a(19) =9310a(20) =10290a(21) =11319a(22) =12397a(23) =13524a(24) =14700a(25) =15925a(26) =17199a(27) =18522a(28) =19894a(29) =21315