S be a set with n elements.
For arbitrary n, the poset is, in fact, a lattice with minimum element and maximum element . We have the recurrence where denotes the Stirling number of the second kind. The paper is unfortunately not yet completed and a detailed report will have to wait. Plouffe gave all known decimal digits in the Inverse Symbolic Calculator pages. The Mathcad PLUS 6.0 file sbsts.mcd verifies the recurrence and asymptotic results given above, and demonstrates how slow the convergence to Lengyel's constant is.