cp's OEIS Frontend

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.

A088713 G.f. A(x) satisfies A(x/A(x)) = 1/(1-x).

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%I A088713 #19 Jan 15 2018 08:52:24
%S A088713 1,1,2,6,24,118,674,4308,30062,225266,1791964,15009118,131566314,
%T A088713 1201452248,11389283418,111761444078,1132680800640,11834071103246,
%U A088713 127261591139010,1406778021294220,15967144849210158,185897394076705298
%N A088713 G.f. A(x) satisfies A(x/A(x)) = 1/(1-x).
%H A088713 Vaclav Kotesovec, <a href="/A088713/b088713.txt">Table of n, a(n) for n = 0..300</a>
%F A088713 G.f. satisfies: A(x) = 1 + x*A(x)*A(1-1/A(x)).
%F A088713 G.f.: A(x*g(x)) = g(x) = (1-1/A(x))/x where g(x) is the g.f. of A088714.
%F A088713 From _Paul D. Hanna_, Dec 06 2009: (Start)
%F A088713 G.f. satisfies: A(x) = 1 + A(x)*Series_Reversion(x/A(x)).
%F A088713 G.f. satisfies: A( (x/(1+x)) / A(x/(1+x)) ) = 1 + x.
%F A088713 (End)
%F A088713 Logarithmic derivative: given g.f. A(x), let G(x) = A(x*G(x)) be the g.f. of A088714, then A'(x)/A(x) = (G(x) + x*G'(x)) / (1 - x*G(x)).
%e A088713 G.f.: A(x) = 1 + x + 2*x^2 + 6*x^3 + 24*x^4 + 118*x^5 + 674*x^6 +...
%e A088713 Illustration of logarithmic derivation.
%e A088713 If we form an array of coefficients of x^k in A(x)^n, n>=1, like so:
%e A088713 A^1: [1],1,  2,   6,   24,   118,   674,    4308, ...;
%e A088713 A^2: [1, 2], 5,  16,   64,   308,  1716,   10724, ...;
%e A088713 A^3: [1, 3,  9], 31,  126,   600,  3278,   20070, ...;
%e A088713 A^4: [1, 4, 14,  52], 217,  1032,  5560,   33440, ...;
%e A088713 A^5: [1, 5, 20,  80,  345], 1651,  8820,   52270, ...;
%e A088713 A^6: [1, 6, 27, 116,  519,  2514],13385,   78420, ...;
%e A088713 A^7: [1, 7, 35, 161,  749,  3689, 19663], 114269, ...; ...
%e A088713 then the sums of the coefficients of x^k, k=0..n-1, in A(x)^n (shown above in brackets) begin:
%e A088713 1 = 1;
%e A088713 1 + 2 = 3;
%e A088713 1 + 3 +  9 = 13;
%e A088713 1 + 4 + 14 +  52 = 71;
%e A088713 1 + 5 + 20 +  80 +  345 = 451;
%e A088713 1 + 6 + 27 + 116 +  519 +  2514 = 3183;
%e A088713 1 + 7 + 35 + 161 +  749 +  3689 + 19663 = 24305; ...
%e A088713 and equal the coefficients in log(A(x)):
%e A088713 log(A(x)) = x + 3*x^2/2 + 13*x^3/3 + 71*x^4/4 + 451*x^5/5 + 3183*x^6/6 + 24305*x^7/7 + 197551*x^8/8 +...
%e A088713 The main diagonal in the above table forms the g.f. G(x) of A088714:
%e A088713 [1/1, 2/2, 9/3, 52/4, 345/5, 2514/6, 19663/7, ...]
%e A088713 where G(x) = 1 + x + 3*x^2 + 13*x^3 + 69*x^4 + 419*x^5 + 2809*x^6 +...
%e A088713 satisfies A'(x)/A(x) = (G(x) + x*G'(x)) / (1 - x*G(x)).
%t A088713 terms = 22; A[_] = 1; Do[A[x_] = 1 + x*A[x]*A[1 - 1/A[x]] + O[x]^j // Normal, {j, terms}]; CoefficientList[A[x], x] (* _Jean-François Alcover_, Jan 15 2018 *)
%o A088713 (PARI) a(n)=local(A=1+x);for(i=1,n,A=(1+A*serreverse(x/(A+x*O(x^n))))^1);polcoeff(A,n)
%o A088713 for(n=0,30,print1(a(n),", ")) \\ _Paul D. Hanna_, Dec 06 2009
%o A088713 (PARI) {a(n)=local(A=1+x);if(n==0,1,for(i=1,n,
%o A088713 A=1+x*exp(sum(k=1,n-1,sum(j=0,k,polcoeff(A^k+x*O(x^j),j))*x^k/k)+x*O(x^n))));
%o A088713 polcoeff(A+x*O(x^n),n)}
%o A088713 for(n=0,30,print1(a(n),", ")) \\ _Paul D. Hanna_, Dec 09 2013
%Y A088713 Cf. A088714.
%Y A088713 Variants: A154677, A168448, A168449, A168478, A168479.
%K A088713 nonn
%O A088713 0,3
%A A088713 _Paul D. Hanna_, Oct 12 2003