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A185331 Riordan array ((1-x+x^2)/(1+x^2), x/(1+x^2)).

%I A185331 #36 Mar 04 2021 19:13:12
%S A185331 1,-1,1,0,-1,1,1,-1,-1,1,0,2,-2,-1,1,-1,1,3,-3,-1,1,0,-3,3,4,-4,-1,1,
%T A185331 1,-1,-6,6,5,-5,-1,1,0,4,-4,-10,10,6,-6,-1,1,-1,1,10,-10,-15,15,7,-7,
%U A185331 -1,1,0,-5,5,20,-20,-21,21,8,-8,-1,1
%N A185331 Riordan array ((1-x+x^2)/(1+x^2), x/(1+x^2)).
%C A185331 Triangle T(n,k), read by rows, given by (-1, 1, -1, 1, 0, 0, 0, 0, 0, 0, 0, ...) DELTA (1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, ...) where DELTA is the operator defined in A084938.
%H A185331 G. C. Greubel, <a href="/A185331/b185331.txt">Table of n, a(n) for the first 100 rows, flattened</a>
%F A185331 T(n,k) = T(n-1,k-1) - T(n-2,k), T(0,0) = 1, T(0,1) = -1, T(0,2) = 0.
%F A185331 G.f.: (1-x+x^2)/(1-y*x+x^2).
%F A185331 Sum_{k, 0<=k<=n} T(n,k)*x^k = (-1)^n*A184334(n), A163805(n), A000007(n), A028310(n), A025169(n-1), A005320(n) (n>0) for x = -1, 0, 1, 2, 3, 4 respectively.
%F A185331 T(n,n) = 1, T(n+1,n) = -1, T(n+2,n) = -n, T(n+3,n) = n+1, T(n+4,n) = n(n+1)/2 = A000217(n).
%F A185331 T(2n,2k) = (-1)^(n-k) * A128908(n,k), T(2n+1,2k+1) = -T(2n+1,2k) = A129818(n,k), T(2n+2,2k+1) = (-1)*A053122(n,k). - _Philippe Deléham_, Feb 09 2012
%e A185331 Triangle begins:
%e A185331    1;
%e A185331   -1,  1;
%e A185331    0, -1,   1;
%e A185331    1, -1,  -1,   1;
%e A185331    0,  2,  -2,  -1,   1;
%e A185331   -1,  1,   3,  -3,  -1,   1;
%e A185331    0, -3,   3,   4,  -4,  -1,   1;
%e A185331    1, -1,  -6,   6,   5,  -5,  -1,  1;
%e A185331    0,  4,  -4, -10,  10,   6,  -6, -1,  1;
%e A185331   -1,  1,  10, -10, -15,  15,   7, -7, -1,  1;
%e A185331    0, -5,   5,  20, -20, -21,  21,  8, -8, -1,  1;
%e A185331    1, -1, -15,  15,  35, -35, -28, 28,  9, -9, -1, 1;
%t A185331 CoefficientList[Series[CoefficientList[Series[(1 - x + x^2)/(1 - y*x + x^2), {x, 0, 10}], x], {y, 0, 10}], y] // Flatten (* _G. C. Greubel_, Jun 27 2017 *)
%Y A185331 Cf. A206474 (unsigned version).
%Y A185331 Cf. A007318, A053122, A078812, A085478, A128908, A129818,
%K A185331 easy,sign,tabl
%O A185331 0,12
%A A185331 _Philippe Deléham_, Feb 08 2012