a(n) = Sum_{k=0..3} binomial(6,k)*binomial(n,k).

Terms

a(0) =1a(1) =7a(2) =28a(3) =84a(4) =195a(5) =381a(6) =662a(7) =1058a(8) =1589a(9) =2275a(10) =3136a(11) =4192a(12) =5463a(13) =6969a(14) =8730a(15) =10766a(16) =13097a(17) =15743a(18) =18724a(19) =22060a(20) =25771a(21) =29877a(22) =34398a(23) =39354a(24) =44765a(25) =50651a(26) =57032a(27) =63928a(28) =71359a(29) =79345