OFFSET
0,6
LINKS
Wikipedia, Partition of a set
EXAMPLE
a(4) = 1: {{1,6}, {2,5}, {3,8}, {4,7}}.
a(5) = 2: {{1,6}, {2,9}, {3,10}, {4,7}, {5,8}}, {{1,6}, {2,5}, {3,8}, {4,9}, {7,10}}.
MAPLE
b:= proc(s) option remember; `if`(s={}, 1, (j-> add(`if`(i<j and
andmap(isprime, [j+i, j-i]), b(s minus {i, j}), 0), i=s))(max(s)))
end:
a:= n-> b({$1..2*n}):
seq(a(n), n=0..15);
MATHEMATICA
b[s_] := b[s] = If[s == {}, 1, With[{j = Max[s]}, Sum[If[i < j && AllTrue[{j+i, j-i}, PrimeQ], b[s ~Complement~ {i, j}], 0], {i, s}]]];
a[n_] := b[Range[2n]];
a /@ Range[0, 15] (* Jean-François Alcover, Aug 25 2021, after Alois P. Heinz *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Alois P. Heinz, Mar 01 2021
EXTENSIONS
a(25)-a(35) from Bert Dobbelaere, Mar 06 2021
STATUS
approved