A257019 Numbers whose quarter-square representation consists of two terms.

3, 5, 7, 8, 10, 11, 13, 14, 17, 18, 21, 22, 24, 26, 27, 29, 31, 32, 34, 37, 38, 40, 43, 44, 46, 48, 50, 51, 53, 55, 57, 58, 60, 62, 65, 66, 68, 70, 73, 74, 76, 78, 82, 83, 85, 87, 91, 92, 94, 96, 99, 101, 102, 104, 106, 109, 111, 112, 114, 116, 119, 122, 123

Offset: 1

Author

Clark Kimberling, Apr 15 2015

Keywords

• nonn
• easy

Comments

Every positive integer is a sum of at most four distinct quarter squares (see A257019).

Examples

			Quarter-square representations:
r(0) = 0, one term
r(1) = 1, one term
r(3) = 2 + 1, two terms, so a(1) = 3
		

Links

• Clark Kimberling, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A002620, A257020, A257021, A257023.

Programs

Mathematica

z = 100; b[n_] := Floor[(n + 1)^2/4]; bb = Table[b[n], {n, 0, 100}];
s[n_] := Table[b[n], {k, b[n + 1] - b[n]}];
h[1] = {1}; h[n_] := Join[h[n - 1], s[n]];
g = h[100]; r[0] = {0};
r[n_] := If[MemberQ[bb, n], {n}, Join[{g[[n]]}, r[n - g[[n]]]]];
u = Table[Length[r[n]], {n, 0, 4 z}];(* A257023 *)
Flatten[-1 + Position[u, 1]]; (* A002620 *)
Flatten[-1 + Position[u, 2]]; (* A257019 *)
Flatten[-1 + Position[u, 3]]; (* A257020 *)
Flatten[-1 + Position[u, 4]]; (* A257021 *)