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 A204857 #10 Dec 19 2017 14:11:02
%S A204857 1,1,1,3,5,11,27,61,151,375,1001,2699,7635,22069,65695,199671,620417,
%T A204857 1966715,6367323,21059149,71216311,246322503,871268465,3148964147,
%U A204857 11613253707,43625643373,166606282471,645633978279,2534590357457,10066575332603
%N A204857 G.f.: Sum_{n>=0} n!*x^(n*(n+1)/2) / Product_{k=1..n} (1 - (n-k+1)*x^k).
%H A204857 Vaclav Kotesovec, <a href="/A204857/b204857.txt">Table of n, a(n) for n = 0..250</a>
%e A204857 G.f.: A(x) = 1 + x + x^2 + 3*x^3 + 5*x^4 + 11*x^5 + 27*x^6 + 61*x^7 +...
%e A204857 where A(x) = 1 + x/(1-x) + 2!*x^3/((1-2*x)*(1-x^2)) + 3!*x^6/((1-3*x)*(1-2*x^2)*(1-x^3)) + 4!*x^10/((1-4*x)*(1-3*x^2)*(1-2*x^3)*(1-x^4)) +...
%t A204857 Table[SeriesCoefficient[Sum[n!*x^Binomial[n + 1, 2]/Product[(1 - (n - k + 1)*x^k), {k, 1, n}], {n, 0, 100}], {x, 0, n}], {n, 0, 50}] (* _G. C. Greubel_, Dec 19 2017 *)
%o A204857 (PARI) {a(n)=polcoeff(1+sum(m=1,n,m!*x^(m*(m+1)/2)/prod(k=1,m,1-(m-k+1)*x^k+x*O(x^n))),n)}
%Y A204857 Cf. A204858, A204855.
%K A204857 nonn
%O A204857 0,4
%A A204857 _Paul D. Hanna_, Jan 20 2012