a(n) = ceiling(a(n-1)/(2^(1/3)-1)+1), a(1)=1.

Terms

a(0) =1a(1) =5a(2) =21a(3) =82a(4) =317a(5) =1221a(6) =4699a(7) =18080a(8) =69561a(9) =267625a(10) =1029641a(11) =3961362a(12) =15240637a(13) =58635641a(14) =225590199a(15) =867918160a(16) =3339160721a(17) =12846826845a(18) =49425880861a(19) =190157283842a(20) =731596320957