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

Terms

a(0) =1a(1) =2a(2) =7a(3) =22a(4) =69a(5) =208a(6) =634a(7) =1903a(8) =5734a(9) =17210a(10) =51702a(11) =155107a(12) =465561a(13) =1396684a(14) =4190689a(15) =12572144a(16) =37718360a(17) =113155081a(18) =339471195a(19) =1018413586a(20) =3055258062a(21) =9165774828a(22) =27497376189a(23) =82492128568a(24) =247476542954a(25) =742429628932