%N Coins left after packing X patterns into an n X n array of coins.
%C The X pattern (8c5s2 type) is a pattern in which 8 curves cover 5 coins, and is one of a total of 13 such distinct patterns that appear in a tightly-packed 3 X 3 square array of coins of identical size; each of the 8 curves is a circular arc lying along the edge of one of the 5 coins, and the 8 curves are joined end-to-end to form a continuous area.
%C a(n) is the total number of coins left (the coins out side X patterns) after packing X patterns into an n X n array of coins. The maximum number of X patterns that can be packed into an n X n array of coins is A231056 and voids left is A231065.
%C a(n) is also the total number of coins left after packing "+" patterns (8c5s1 type) into an n X n array of coins. See illustration in links.
%H Kival Ngaokrajang, <a href="/A231064/a231064_1.pdf">Illustration of initial terms (U)</a>
%F Empirical g.f.: x^2*(5*x^15 -5*x^14 -5*x^12 +5*x^11 -5*x^10 +5*x^9 +4*x^5 +x^4 +4*x^3 +7*x^2 +4) / ((x -1)^2*(x^4 +x^3 +x^2 +x +1)). - _Colin Barker_, Nov 27 2013
%o (Small Basic)
%o x = 0
%o d1 = 1
%o For n = 2 To 100
%o If Math.Remainder(n+2,5) = 1 Then
%o d2 = 0
%o If Math.Remainder(n+2,5) = 4 Then
%o d2 = -1
%o d2 = 1
%o d1[n+2] = d1[n+1] + d2
%o x[n+1] = x[n] + d1[n+1]
%o If n >= 13 And Math.Remainder(n,5) = 3 Then
%o x[n] = x[n] - 1
%o If n=6 or n>=16 And Math.Remainder(n,5)=1 Then
%o x[n] = x[n] + 1
%o U = n*n - x[n]*5
%o TextWindow.Write(U+", ")
%Y Cf. A008795, A230370 (3-curves); A074148, A227906, A229093, A229154 (4-curves); A001399, A230267, A230276 (5-curves); A229593, A228949, A229598, A002620, A230548, A230549, A230550 (6-curves).
%A _Kival Ngaokrajang_, Nov 03 2013