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 A159309 #2 Mar 30 2012 18:37:17
%S A159309 1,3,10,35,116,606,2990,11203,65368,567558,3229942,12730946,78628616,
%T A159309 666394746,3968286590,21143707843,160244432497,1602468019110,
%U A159309 20852615681805,320475672814590,4102188681702086,36438823274699332
%N A159309 L.g.f.: Sum_{n>=1} a(n)*x^n/n = Sum_{n>=1} (1 + sigma(n)*x)^n * x^n/n.
%F A159309 a(n) = n * Sum_{k=0..[n/2]} C(n-k,k)*sigma(n-k)^k/(n-k) for n>=1.
%e A159309 L.g.f.: L(x) = x + 3*x^2/2 + 10*x^3/3 + 35*x^4/4 + 116*x^5/5 +...
%e A159309 L(x) = (1+x)*x + (1+3*x)^2*x^2/2 + (1+4*x)^3*x^3/3 + (1+7*x)^4*x^4/4 +...
%e A159309 exp(L(x)) = 1 + x + 2*x^2 + 5*x^3 + 14*x^4 + 40*x^5 + 154*x^6 +... (A159308).
%o A159309 (PARI) {a(n)=n*polcoeff(sum(m=1,n+1,(1+sigma(m)*x+x*O(x^n))^m*x^m/m),n)}
%o A159309 (PARI) {a(n)=n*sum(k=0,n\2,binomial(n-k,k)*sigma(n-k)^k/(n-k))}
%Y A159309 Cf. A159308 (exp).
%K A159309 nonn
%O A159309 1,2
%A A159309 _Paul D. Hanna_, Apr 10 2009