%I #12 Jun 20 2022 13:16:23

%S 0,2,-1,5,-2,8,-5,21,-8,34,-21,81,-34,128,-81,337,-128,546,-337,1301,

%T -546,2056,-1301,5381,-2056,8706,-5381,20737,-8706,32768,-20737,86273,

%U -32768,139778,-86273,333061,-139778,526344,-333061,1377557,-526344,2228770

%N First differences of A006921.

%H Reinhard Zumkeller, <a href="/A257971/b257971.txt">Table of n, a(n) for n = 0..1000</a>

%F a(2*n) = - A168081(n), a(2*n+1) = A168081(n+2);

%F a(2*n+4) = - a(2*n+1).

%o (Haskell)

%o a257971 n = a257971_list !! n

%o a257971_list = zipWith (-) (tail a006921_list) a006921_list

%o (Python)

%o def A257971(n): return sum(int(not r & ~(n+2-r))*2**(n//2+1-r) for r in range(n//2+2)) if n & 1 else -sum(int(not r & ~(n-1-r))*2**(n//2-1-r) for r in range(n//2)) # _Chai Wah Wu_, Jun 20 2022

%Y Cf. A006911, A168081.

%K sign

%O 0,2

%A _Reinhard Zumkeller_, Jul 14 2015