[tromp]

Thanks for showing the syntax to use! I computed the number of closed lambda terms of size 10 bits within 0 binders with nclosed(k=0, n=10) :

    function nclosed(k:number, n:number) {
      if (n < 2) return 0;
      let sum = nclosed(k+1,n-2); // Lambda
      for (let i = 2; i < n-1; i++) {
        sum += nclosed(k,i) * nclosed(k,n-2-i); // Application
      }
      if (n-2 < k) sum += 1;      // Variable
      return sum;
    }