

A020916


A molecule is a row of atoms joined together by bonds; each atom has a valence (e.g., 13=2 is a molecule with 3 atoms); a(n) is the number of molecules with n atoms and different valencies from 1 to n.


1



0, 0, 0, 1, 2, 0, 0, 24, 96, 0, 0, 10000, 60736, 0, 0, 20511168, 168661760, 0, 0, 134002359296, 1398597049856, 0, 0, 2146989255011328, 27232259080056832, 0, 0
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OFFSET

0,5


COMMENTS

a(n)=0 whenever A000217(n) is odd, because sum of atoms must be twice the sum of the bonds and both are integers. Full explanation on Munafo web page.  Robert Munafo, Jun 22 2009


LINKS



EXAMPLE

For n=4 the a(4)=2 solutions are 124*3 and 13=4=2 (where * is a triple bond).  Robert Munafo, Jun 22 2009


CROSSREFS



KEYWORD

nonn,more


AUTHOR

Mario Velucchi (mathchess(AT)velucchi.it)


EXTENSIONS



STATUS

approved



