X :=
proc(h,m)
option remember;
local n;

    if m=1 then if h=0 then return 0 else return 1 fi fi;

    n:=m-1;

    1/n*
    add(add(X(h,q)*
            `if`(n-q+1 mod l =0, (n-q+1)/l*X(h-1,(n-q+1)/l), 0),
            q=1..n), l=1..n);

end;

XX := (h,m)-> X(h,m)-X(h-1,m);