a(n) = 49*(n-1)*(n-2)/2.

Terms

a(0) =49a(1) =147a(2) =294a(3) =490a(4) =735a(5) =1029a(6) =1372a(7) =1764a(8) =2205a(9) =2695a(10) =3234a(11) =3822a(12) =4459a(13) =5145a(14) =5880a(15) =6664a(16) =7497a(17) =8379a(18) =9310a(19) =10290a(20) =11319a(21) =12397a(22) =13524a(23) =14700a(24) =15925a(25) =17199a(26) =18522a(27) =19894a(28) =21315a(29) =22785