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

Terms

a(0) =1a(1) =1a(2) =2a(3) =5a(4) =13a(5) =35a(6) =92a(7) =246a(8) =646a(9) =1705a(10) =4475a(11) =11755a(12) =30790a(13) =80738a(14) =211424a(15) =553780a(16) =1449999a(17) =3796903a(18) =9940710a(19) =26027151a(20) =68140743a(21) =178399767a(22) =467059142a(23) =1222789414a(24) =3201309100a(25) =8381170779a(26) =21942203523a(27) =57445520528a(28) =150394362117a(29) =393737778753