%I
%S 1,5,13,23,37,55,75,95,127,157,185,227,263,305,357,403,455,511,571,
%T 631,703,769,833,923,997,1069,1169,1245,1329,1443,1535,1631,1743,1849,
%U 1957,2075,2195,2307,2439,2565,2683,2845,2957,3097,3265,3385
%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(2n1) 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.
%K nonn
%O 1,2
%A _Hugo Pfoertner_, Nov 13 2004
