OFFSET
0,2
FORMULA
Conjecture: a(n) = (n^2 + 3n + 5 - (-1)^n)/2 for n > 1.
Conjecture: a(n) = 2*a(n-1)-2*a(n-3)+a(n-4) for n>5. G.f.: (x^5-x^4-x^2+2*x+1) / ((x-1)^3*(x+1)). - Colin Barker, Aug 01 2013
EXAMPLE
Three tetrahedra labeled (1, 2, 8, 12) yield the 20 possible sums 3, 4, 5, 6, 10, 11, 12, 14, 15, 16, 17, 18, 21, 22, 24, 25, 26, 28, 32, 36. No more sums can be obtained by different labelings, and no labeling with labels < 12 yields 20 possible sums. Therefore a(3) = 12.
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Jens Voß, Jul 17 2013
STATUS
approved