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a(0) = 0, a(1) = 1 and for n > 1, a(n) = sum of all previous terms.
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%I #42 Jul 27 2024 09:40:50

%S 0,1,1,2,4,8,16,32,64,128,256,512,1024,2048,4096,8192,16384,32768,

%T 65536,131072,262144,524288,1048576,2097152,4194304,8388608,16777216,

%U 33554432,67108864,134217728,268435456,536870912,1073741824,2147483648,4294967296,8589934592

%N a(0) = 0, a(1) = 1 and for n > 1, a(n) = sum of all previous terms.

%C Essentially a duplicate of A000079. - _N. J. A. Sloane_, Oct 15 2009

%C a(n) is the number of compositions of n into an odd number of parts.

%C Also 0 together with A011782. - _Omar E. Pol_, Oct 28 2013

%C Inverse INVERT transform of A001519. - _R. J. Mathar_, Dec 08 2022

%H Indranil Ghosh, <a href="/A166444/b166444.txt">Table of n, a(n) for n = 0..3317</a>

%H <a href="/index/Rec#order_01">Index entries for linear recurrences with constant coefficients</a>, signature (2).

%F a(n) = A000079(n-1) for n > 0.

%F O.g.f.: x*(1 - x) / (1 - 2*x) = x / (1 - x / (1 - x)).

%F a(n) = (1-n) * a(n-1) + 2 * Sum_{k=1..n-1} a(k) * a(n-k) if n>1. - _Michael Somos_, Jul 23 2011

%F E.g.f.: (exp(2*x) + 2*x - 1)/4. - _Stefano Spezia_, Aug 07 2022

%e G.f. = x + x^2 + 2*x^3 + 4*x^4 + 8*x^5 + 16*x^6 + 32*x^7 + 64*x^8 + 128*x^9 + ...

%p a:= n-> `if`(n<2, n, 2^(n-2)):

%p seq(a(n), n=0..40); # _Alois P. Heinz_, Jun 02 2021

%t a[0] = 0; a[1] = 1; a[n_] := a[n] = Plus @@ Array[a, n - 1]; Array[a, 35, 0]

%o (Magma) [n le 1 select n else 2^(n-2): n in [0..40]]; // _G. C. Greubel_, Jul 27 2024

%o (SageMath) [(2^n +2*int(n==1) -int(n==0))/4 for n in range(41)] # _G. C. Greubel_, Jul 27 2024

%Y Cf. A000045, A000079, A000213, A000288, A000322, A000383, A001519.

%Y Cf. A011782, A034008, A060455, A123526, A127193, A127194, A127624.

%Y Cf. A131577, A163551.

%K nonn,easy

%O 0,4

%A _Robert G. Wilson v_, Oct 13 2009