Created
July 31, 2018 18:35
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Calculate Bell numbers.
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| # https://en.wikipedia.org/wiki/Partition_of_a_set#Counting_partitions | |
| bell = function(n) { | |
| ifelse(n > 0, | |
| sum(Vectorize(function(n, k) { | |
| choose(n - 1, k) * bell(k) | |
| }, "k")(n, 0:(n - 1))), | |
| 1) | |
| } | |
| bell(5) |
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