Odd problem with sequence A108247
Brendan McKay
bdm at cs.anu.edu.au
Sun Apr 1 15:06:08 CEST 2007
Hello, there is a problem with sequence A108247.
A108247 Number of 3-regular (trivalent) labeled graphs on 2n
vertices with multiple edges and loops allowed.
1, 1, 10, 760, 190050, 103050570, 102359800620, 168076482974400, ...
Linear recurrence satisfied by a(n) {a(0) = 1, a(3) = 4720, a(4) =
1256395, a(5) = 699971370, a(1) = 2, a(2) = 47, and ...
See the problem? The initial values in the Linear recurrence are
1, 2, 4720, 1256395, 699971370, ...
which are not the same as listed for this sequence.
My computations suggest that 1, 2, 4720, 1256395, 699971370, ...
matches the definition precisely. In fact it is A005814
"Number of trivalent labeled graphs with 2n nodes."
So what does 1, 1, 10, 760, 190050, ... count?
Brendan.
CC: contributor Marni Marsha
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