OFFSET
1,1
COMMENTS
a(n) are even R that give a(n) >= 2, which seems to be nonperiodic, for even R there is no contact point exist. This is the case of A053417.
Sequence A053416 addresses the case in which the center of the R-circle (R = r*n) is chosen at a lattice point instead; in that case, the number of contact points is 0 and 6 for even n > 0 and odd n > 1, respectively.
See illustrations in links.
LINKS
Kival Ngaokrajang, Illustration R-circle center is at (0.5,0)
Kival Ngaokrajang, Illustration R-circle center is at (0,0)
PROG
(Small Basic)
For r = 2 To 1000 Step 2
c = 0
imax = math.Floor((r-1)/math.Power(3, 0.5))
for i = 0 to imax
If Math.Remainder(i, 2) = 1 then
j = Math.Power(((r-1)*(r-1)-3*i*i)/4, 0.5)
Else
j = (Math.Power((r-1)*(r-1)-3*i*i, 0.5)+1)/2
EndIf
If j-math.Floor(j) = 0 Then
If i = 0 Then
c = c + 2
Else
c = c + 4
EndIf
endif
EndFor
TextWindow.Write(c+", ")
EndFor
CROSSREFS
KEYWORD
nonn
AUTHOR
Kival Ngaokrajang, Apr 06 2014
STATUS
approved