OFFSET
0,5
COMMENTS
Reference needed! [ N. J. A. Sloane ]
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
Robert Munafo, A Restricted Class of Permutations [From Robert Munafo, Jun 22 2009]
EXAMPLE
For n=4 the a(4)=2 solutions are 1-2-4*3 and 1-3=4=2 (where * is a triple bond). - Robert Munafo, Jun 22 2009
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Mario Velucchi (mathchess(AT)velucchi.it)
EXTENSIONS
a(15)-a(18) from Robert Munafo, Jun 22 2009
a(19)-a(22) from Robert Munafo, Oct 02 2009
a(23)-a(26) from Robert Munafo, Oct 26 2009
STATUS
approved