%N a(n) = the number of ordered pairs of n-bit bit strings, such that both bit strings have at least n/2 one-bits, or both have at most n/2 one-bits.
%F a(n) = 4^n/2 + 2^n*c - c^2/2; where c is (n choose n/2) for even n, 0 for odd n.
%e a(2)=14 because of the 16 ordered pairs, only (00,11) and (11,00) do not qualify.
%A _Jon Perry_, May 31 2003
%E Edited by _Don Reble_, Nov 07 2005