Knopfmacher, A., Odlyzko, A. M., Pittel, B., Richmond, L. B., Stark, D., Szekeres, G. and Wormald, N. C. (1998) “The Asymptotic Number of Set Partitions with Unequal Block Sizes”, The Electronic Journal of Combinatorics, 6(1), p. R2. doi: 10.37236/1434.