math.extras: Fun estimate for factorials from a paper

diff --git a/extra/math/extras/extras.factor b/extra/math/extras/extras.factor
index 434d09aa375522a6e5a862b522e3499c305fe9f4..11f66f1e34304e62d937298d24b7224b98aefbde 100644 (file)
--- a/extra/math/extras/extras.factor
+++ b/extra/math/extras/extras.factor
@@ -42,6 +42,10 @@ PRIVATE>
 MEMO: bernoulli ( p -- n )
     [ 1 ] [ (bernoulli) ] if-zero ;
 
+! From page 4 https://arxiv.org/ftp/arxiv/papers/2201/2201.12601.pdf
+: bernoulli-estimate-factorial ( n -- n! )
+    [ 2pi swap ^ ] [ bernoulli ] bi * 2 / ;
+
 : chi2 ( actual expected -- n )
     0 [ dup 0 > [ [ - sq ] keep / + ] [ 2drop ] if ] 2reduce ;