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 A054949 #18 Aug 27 2019 10:53:12
%S A054949 1,1,19,1612,565276,734799976,3523103676184,63519230066936512,
%T A054949 4400411105398828102336,1190433708177460323642937216,
%U A054949 1270463865199882936737403300783744,5381067966904826663696685903449569172992,90765788839502187660342772995967835888789034496
%N A054949 Number of labeled semi-strong digraphs on n nodes with an odd number of components.
%H A054949 V. A. Liskovets, <a href="http://www.cs.uwaterloo.ca/journals/JIS/VOL3/LISK/Derseq.html">Some easily derivable sequences</a>, J. Integer Sequences, 3 (2000), #00.2.2.
%F A054949 a(n) = (A054948(n) + A054947(n))/2. - _Andrew Howroyd_, Sep 10 2018
%t A054949 A054947[1] = 1; A054947[n_] := A054947[n] = 2^(n(n - 1)) - Sum[Binomial[n, j] 2^((n - 1)(n - j)) A054947[j], {j, 1, n - 1}];
%t A054949 A054948[0] = 1; A054948[n_] := A054948[n] = Module[{A}, A = 1 + Sum[ A054948[k]*x^k/k!, {k, 1, n - 1}]; n!*SeriesCoefficient[Sum[2^(k^2 - k)*x^k/k!/(A /. x -> 2^k*x) , {k, 0, n}], {x, 0, n}]];
%t A054949 a[n_] := (A054948[n] + A054947[n])/2;
%t A054949 Array[a, 13] (* _Jean-François Alcover_, Aug 27 2019 *)
%Y A054949 Cf. A054947, A054948, A054950.
%K A054949 nonn,easy
%O A054949 1,3
%A A054949 _N. J. A. Sloane_, May 24 2000
%E A054949 More terms from _Vladeta Jovovic_, Mar 11 2003