a(n) = binomial(5*(n+1),4)/5, with n >= 0.

Terms

a(0) =1a(1) =42a(2) =273a(3) =969a(4) =2530a(5) =5481a(6) =10472a(7) =18278a(8) =29799a(9) =46060a(10) =68211a(11) =97527a(12) =135408a(13) =183379a(14) =243090a(15) =316316a(16) =404957a(17) =511038a(18) =636709a(19) =784245a(20) =956046a(21) =1154637a(22) =1382668a(23) =1642914a(24) =1938275a(25) =2271776a(26) =2646567a(27) =3065923a(28) =3533244a(29) =4052055