OFFSET
1,3
LINKS
Reinhard Zumkeller, Table of n, a(n) for n = 1..10000
EXAMPLE
MATHEMATICA
amax = 200; xmax = Sqrt[amax] // Ceiling; Clear[f]; f[_] = 0; Do[q = x^2 + x y + y^2; f[q] = f[q] + 1, {x, 0, xmax}, {y, x, xmax}];
A198772 = Select[Range[0, 3 xmax^2], # <= amax && f[#] == 1&] (* Jean-François Alcover, Jun 21 2018 *)
PROG
(Haskell)
a198772 n = a198772_list !! (n-1)
a198772_list = filter ((== 1) . a088534) a003136_list
(Julia)
function isA198772(n)
M = Int(round(2*sqrt(n/3)))
count = 0
for y in 0:M, x in 0:y
n == x^2 + y^2 + x*y && (count += 1)
count == 2 && break
end
return count == 1
end
A198772list(upto) = [n for n in 0:upto if isA198772(n)]
A198772list(193) |> println # Peter Luschny, Mar 17 2018
CROSSREFS
KEYWORD
nonn
AUTHOR
Reinhard Zumkeller, Oct 30 2011
STATUS
approved