a(1) = 1; a(n) = Sum_{k=1..n} a(ceiling((n-1)/k)).

Terms

a(0) =1a(1) =2a(2) =4a(3) =8a(4) =14a(5) =24a(6) =36a(7) =56a(8) =78a(9) =110a(10) =148a(11) =200a(12) =254a(13) =334a(14) =416a(15) =522a(16) =644a(17) =798a(18) =954a(19) =1162a(20) =1372a(21) =1640a(22) =1934a(23) =2284a(24) =2636a(25) =3090a(26) =3556a(27) =4106a(28) =4694a(29) =5394