  As a report of a teaching experience, we analyse Haskell programs computing
two integer sequences: the Hamming sequence and the Ulam sequence. For both of
them, we investigate two strategies of computation: the first is based on
filtering out those natural numbers that do not belong to the sequence, whereas
the second is based on the direct generation of num- bers that belong to the
sequence. Advocating cross-fertilisation among ideas emerging when programming
in different programming paradigms, in the background, we sketch out some
considerations about corresponding C programs solving the same two problems.
