%N (1/2)*number of distinct angular positions under which an observer positioned at the center of an edge of a square lattice can see the (2n)X(2n-1) points symmetrically surrounding his position.
%F This is a bisection of A049690, that is, a(n) = Sum[k=1..2n+1, phi(2k)]. - _Ralf Stephan_, Nov 13, 2004.
%Y See A099957 for further information. Cf. A049687, A049690, A190815.
%A _Hugo Pfoertner_, Nov 13 2004