This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A201701 #38 Mar 16 2025 02:34:53
%S A201701 1,1,0,2,1,0,4,3,0,0,8,8,1,0,0,16,20,5,0,0,0,32,48,18,1,0,0,0,64,112,
%T A201701 56,7,0,0,0,0,128,256,160,32,1,0,0,0,0,256,576,432,120,9,0,0,0,0,0,
%U A201701 512,1280,1120,400,50,1,0,0,0,0,0
%N A201701 Riordan triangle ((1-x)/(1-2*x), x^2/(1-2*x)).
%C A201701 Triangle T(n,k), read by rows, given by (1,1,0,0,0,0,0,0,0,...) DELTA (0,1,-1,0,0,0,0,0,0,0,...) where DELTA is the operator defined in A084938.
%C A201701 Skewed version of triangle in A200139.
%C A201701 Triangle without zeros: A207537.
%C A201701 For the version with negative odd numbered columns, which is Riordan ((1-x)/(1-2*x), -x^2/(1-2*x)) see comments on A028297 and A039991. - _Wolfdieter Lang_, Aug 06 2014
%C A201701 This is an example of a stretched Riordan array in the terminology of Section 2 of Corsani et al. - _Peter Bala_, Jul 14 2015
%H A201701 C. Corsani, D. Merlini, and R. Sprugnoli, <a href="http://dx.doi.org/10.1016/S0012-365X(97)00110-6">Left-inversion of combinatorial sums</a>, Discrete Mathematics, 180 (1998) 107-122.
%F A201701 T(n,k) = 2*T(n-1,k) + T(n-2,k-1) with T(0,0) = T(1,0) = 1, T(1,1) = 0 and T(n,k) = 0 for k<0 or for n<k.
%F A201701 Sum_{k=0..n} T(n,k)^2 = A002002(n) for n>0.
%F A201701 Sum_{k=0..n} T(n,k)*x^k = A138229(n), A006495(n), A138230(n), A087455(n), A146559(n), A000012(n), A011782(n), A001333(n), A026150(n), A046717(n), A084057(n), A002533(n), A083098(n), A084058(n), A003665(n), A002535(n), A133294(n), A090042(n), A125816(n), A133343(n), A133345(n), A120612(n), A133356(n), A125818(n) for x = -6,-5,-4,-3,-2,-1,0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17 respectively.
%F A201701 G.f.: (1-x)/(1-2*x-y*x^2). - _Philippe Deléham_, Mar 03 2012
%F A201701 From _Peter Bala_, Jul 14 2015: (Start)
%F A201701 Factorizes as A034839 * A007318 = (1/(1 - x), x^2/(1 - x)^2) * (1/(1 - x), x/(1 - x)) as a product of Riordan arrays.
%F A201701 T(n,k) = Sum_{i = k..floor(n/2)} binomial(n,2*i) *binomial(i,k). (End)
%e A201701 The triangle T(n,k) begins:
%e A201701 n\k 0 1 2 3 4 5 6 7 8 9 10 11 ...
%e A201701 0: 1
%e A201701 1: 1 0
%e A201701 2: 2 1 0
%e A201701 3: 4 3 0 0
%e A201701 4: 8 8 1 0 0
%e A201701 5: 16 20 5 0 0 0
%e A201701 6: 32 48 18 1 0 0 0
%e A201701 7: 64 112 56 7 0 0 0 0
%e A201701 8: 128 256 160 32 1 0 0 0 0
%e A201701 9: 256 576 432 120 9 0 0 0 0 0
%e A201701 10: 512 1280 1120 400 50 1 0 0 0 0 0
%e A201701 11: 1024 2816 2816 1232 220 11 0 0 0 0 0 0
%e A201701 ... reformatted and extended. - _Wolfdieter Lang_, Aug 06 2014
%t A201701 (* The function RiordanArray is defined in A256893. *)
%t A201701 RiordanArray[(1 - #)/(1 - 2 #)&, #^2/(1 - 2 #)&, 11] // Flatten (* _Jean-François Alcover_, Jul 16 2019 *)
%Y A201701 Columns include A011782, A001792, A001793, A001794, A006974, A006975, A006976.
%Y A201701 Diagonals sums are in A052980.
%Y A201701 Cf. A028297, A081265, A124182, A131577, A039991 (zero-columns deleted, unsigned and zeros appended).
%Y A201701 Cf. A098158, A200139, A207537.
%Y A201701 Cf. A028297 (signed version, zeros deleted). Cf. A034839.
%K A201701 nonn,easy,tabl
%O A201701 0,4
%A A201701 _Philippe Deléham_, Dec 03 2011
%E A201701 Name changed, keyword:easy added, crossrefs A028297 and A039991 added, and g.f. corrected by _Wolfdieter Lang_, Aug 06 2014