[seqfan] exp(sin(x))

franktaw at netscape.net franktaw at netscape.net
Thu Apr 29 14:27:53 CEST 2010


A003724, the number of set partitions of n objects into odd blocks, is 
the exponential expansion of exp(sinh(x)).

It appears that A002017, the expansion of exp(sin(x)), is the number of 
set partitions of n objects with an even number of parts of size == 3 
(mod 4), minus the number of such partitions with an odd number of 
parts of size == 3 (mod 4). I have manually verified this through n = 
8. Can someone confirm (i.e., prove) it?

Franklin T. Adams-Watters




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