a(n) = floor((n^2 + 1)/5).

Terms

a(0) =0a(1) =0a(2) =1a(3) =2a(4) =3a(5) =5a(6) =7a(7) =10a(8) =13a(9) =16a(10) =20a(11) =24a(12) =29a(13) =34a(14) =39a(15) =45a(16) =51a(17) =58a(18) =65a(19) =72a(20) =80a(21) =88a(22) =97a(23) =106a(24) =115a(25) =125a(26) =135a(27) =146a(28) =157a(29) =168