A225530 - OEIS

%I #15 Aug 02 2019 03:25:05

%S 1,2,1,2,2,4,2,6,4,6,4,10,4,12,6,8,8,16,6,18,8,12,10,22,8,20,12,18,12,

%T 28,8,30,16,20,16,24,12,36,18,24,16,40,12,42,20,24,22,46,16,42,20,32,

%U 24,52,18,40,24,36,28,58,16,60,30,36,32,48,20,66

%N Number of ordered pairs (i,j) with i,j >= 0, i + j = n and gcd(i,j) <= 1.

%C This sequence is in reply to an extension request made in A100449.

%C Note that gcd(0,m) = m for any m.

%C Apparently a(n) = A000010(n), n >= 2. - _R. J. Mathar_, May 11 2013

%H Robert Price, <a href="/A225530/b225530.txt">Table of n, a(n) for n = 0..400</a>

%t f[n_]:=Length[Complement[Union[Flatten[Table[If[i+j==n&&GCD[i, j]<=1, {i,j}], {i, 0, n}, {j, 0, n}], 1]], {Null}]]; Table[f[n], {n, 0, 100}]

%Y Cf. A018805, A027430, A100448, A100449, A100450, A213207, A213208, A213212, A213213.

%K nonn,easy

%O 0,2

%A _Robert Price_, May 09 2013