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 A352173 #29 Jun 10 2024 08:50:55 %S A352173 1,2,7,23,85,340,1517,7489,41276,252410,1706071,12660012,102447112, %T A352173 898081422,8477941776,85729296020,924345402273,10584325318278, %U A352173 128259347448244,1639694094741643,22053783907891362,311294619360437722,4601020643330758040,71063337073204684379,1144820435086864897289 %N A352173 The number of Feynman graphs in phi^4 theory with n vertices, 2 external legs. %C A352173 The generating function of this is the product of the g.f. of the connected diagrams (A352174) by the g.f. of the vacuum diagrams (A129429, including a term x^0 for the empty graph): x + 2*x^2 + 7*x^3 + 23*x^4 + ... = (x + x^2 + 3*x^3 + 10*x^4 + ...) * (1 + x + 3*x^2 + 7*x^3 + 20*x^4 + ...). - _R. J. Mathar_, Mar 05 2023 %C A352173 a(n) is the number of multigraphs with n unlabeled nodes of degree 4 plus 2 noninterchangeable nodes of degree 1, loops allowed. - _Andrew Howroyd_, Mar 10 2023 %H A352173 R. de Mello Koch and S. Ramgoolam, <a href="https://doi.org/10.1103/PhysRevD.85.026007">Strings from Feynman graph counting: Without large N</a>, Phys. Rev. D 85 (2012) 026007, App. D. %Y A352173 Cf. A352174 (connected), A129429 (0 ext. legs), A352175 (degree 3 case). %K A352173 nonn %O A352173 0,2 %A A352173 _R. J. Mathar_, Mar 07 2022 %E A352173 Offset corrected and a(13) and beyond from _Andrew Howroyd_, Mar 10 2023