A209978 a(n) = A196227(n)/2.

0, 0, 1, 4, 7, 14, 17, 28, 35, 46, 53, 72, 79, 102, 113, 128, 143, 174, 185, 220, 235, 258, 277, 320, 335, 374, 397, 432, 455, 510, 525, 584, 615, 654, 685, 732, 755, 826, 861, 908, 939, 1018, 1041, 1124, 1163, 1210, 1253, 1344, 1375, 1458, 1497

Offset: 0

Author

Clark Kimberling, Mar 16 2012

Keywords

• nonn

Comments

See A210000 for a guide to related sequences.

Crossrefs

Cf. A196227, A210000.

Programs

Maple

a:= proc(n) option remember; `if`(n<2, 0,
      a(n-1)-1 + 2*numtheory[phi](n))
    end:
seq(a(n), n=0..60);  # Alois P. Heinz, May 05 2020

Mathematica

a = 1; b = n; z1 = 50;
t[n_] := t[n] = Flatten[Table[w*z - x*y, {w, a, b}, {x, a, b}, {y, a, b}, {z, a, b}]]
c[n_, k_] := c[n, k] = Count[t[n], k]
Table[c[n, 0], {n, 0, z1}]  (* A134506 *)
Table[c[n, 1], {n, 0, z1}]  (* A196227 *)
%/2                         (* A209978 *)
Table[2 c[n, 1], {n, 0, z1}](* A209979 *)
Table[c[n, 2], {n, 0, z1}]  (* A197168 *)
%/2                         (* A209980 *)
Table[c[n, 3], {n, 0, z1}]  (* A210001 *)
Table[c[n, 4], {n, 0, z1}]  (* A210002 *)
Table[c[n, 5], {n, 0, z1}]  (* A210027 *)