%I #23 Oct 04 2023 03:53:38

%S 0,2,10,39,150,545,2010,7320,26880,98775,365010,1353185,5038950,

%T 18830145,70623958,265737270,1002976350,3796197160,14406059010,

%U 54801140307,208932573650,798218035245,3055417070010,11716354754030,45002103387120,173117601112575

%N a(n) = (1/n) * Sum_{d|n} mu(n/d)*(4^d - 3^d - 2^d + 1).

%H Seiichi Manyama, <a href="/A295521/b295521.txt">Table of n, a(n) for n = 1..1666</a>

%H Wikipedia, <a href="https://en.wikipedia.org/wiki/M%C3%B6bius_function">Möbius function</a>

%F a(n) = A027377(n) - A027376(n) - A001037(n) for n > 1.

%t a[n_] := DivisorSum[n, MoebiusMu[n/#] * (4^# - 3^# - 2^# + 1) &] / n; Array[a, 26] (* _Amiram Eldar_, Oct 04 2023 *)

%o (PARI) {a(n) = sumdiv(n, d, moebius(n/d)*(4^d-3^d-2^d+1))/n}

%Y Cf. A001037, A008683, A020988, A027376, A027377.

%K nonn

%O 1,2

%A _Seiichi Manyama_, Nov 23 2017