OFFSET
0,5
LINKS
Mathematics Stack Exchange, Placing the integers {1,2,...,n} on a circle (for n>1) in some special order
EXAMPLE
Out of the 3 essentially different arrangements (1, 2, 3, 4), (1, 2, 4, 3), (1, 3, 2, 4) of four points on a circle, only (1, 2, 3, 4) and (1, 3, 2, 4) yield all sums in {1, ..., 10}, so a(4) = 2.
MATHEMATICA
ok[w_] := Block[{v = Join[w, w], n = Length@w}, n(n+1)/2 == Length@ Union@ Flatten@ Table[ Total@ Take[v, {i, i+k}], {i, n}, {k, 0, n-1}]]; a[n_] := If[n<3, 1, Sum[ Length@ Select[ Permutations@ Complement[ Range@n, e], ok@ Join[e, #] &], {e, Flatten[ Table[{a, 1, b}, {a, 2, n}, {b, a+1, n}], 1]}]]; a /@ Range[0, 9] (* Giovanni Resta, Apr 21 2016 *)
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Jens Voß, Apr 21 2016
EXTENSIONS
a(15) from Giovanni Resta, Apr 21 2016
a(16) from Giovanni Resta, Apr 22 2016
STATUS
approved