login
a(n) = ( (-1)^(n-1) * Sum_{k=0..n-1} (-1)^k*10^(2^k) - (1-(-1)^n)/2 )/9.
7

%I #36 May 07 2021 05:09:20

%S 0,1,10,1101,11110010,1111111100001101,

%T 11111111111111110000000011110010,

%U 1111111111111111111111111111111100000000000000001111111100001101

%N a(n) = ( (-1)^(n-1) * Sum_{k=0..n-1} (-1)^k*10^(2^k) - (1-(-1)^n)/2 )/9.

%H Seiichi Manyama, <a href="/A325910/b325910.txt">Table of n, a(n) for n = 0..10</a>

%F a(n) = -a(n-1) + (10^(2^(n-1)) - 1)/9.

%F a(n) = A007088(A325912(n-1) - (n mod 2)) for n > 0.

%e 1 = -0 + 1.

%e 10 = -1 + 11.

%e 1101 = -10 + 1111.

%e 11110010 = -1101 + 11111111.

%e 1111111100001101 = -11110010 + 1111111111111111.

%e ================================================

%e n | (a(n))_2 | A325912(n-1)

%e --+------------------------------+-------------

%e 1 | 1 = 1 | 2

%e 2 | (10)_2 = 2 | 2

%e 3 | (1101)_2 = 13 | 14

%e 4 | (11110010)_2 = 242 | 242

%e 5 | (1111111100001101)_2 = 65293 | 65294

%t a[n_] := ((-1)^(n - 1) * Sum[(-1)^k * 10^(2^k), {k, 0, n - 1} ] - (1 - (-1)^n)/2)/9; Array[a, 8, 0] (* _Amiram Eldar_, May 07 2021 *)

%o (PARI) {a(n) = ((-1)^(n-1)*sum(k=0, n-1, (-1)^k*10^2^k)-(1-(-1)^n)/2)/9}

%Y Cf. A002275, A007088, A325906, A325912.

%K nonn

%O 0,3

%A _Seiichi Manyama_, Sep 08 2019