OFFSET
0,4
COMMENTS
See A210000 for a guide to related sequences.
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 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Clark Kimberling, Mar 16 2012
STATUS
approved