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 A380269 #8 Jan 23 2025 00:42:37
%S A380269 4,5,6,7,8,13,15,16,28,30
%N A380269 The minimal rank of an n-universal Z-lattice.
%C A380269 a(n) is the least positive integer k such that there exists a positive definite Z-lattice of rank k which represents all positive definite Z-lattices of rank n.
%C A380269 Byeong-Kweon Oh gives the lower bound a(24) >= 6673.
%H A380269 Daejun Kim and Byeong-Kweon Oh, <a href="https://doi.org/10.1007/s11139-020-00314-6">Representations of finite number of quadratic forms with same rank</a>, Ramanujan J., 56 (2021), no. 2, 631-644.
%H A380269 Byeong-Kweon Oh, <a href="https://doi.org/10.1090/S0002-9939-99-05254-5">Universal Z-lattices of minimal rank</a>, Proc. Amer. Math. Soc., 128 (2000), no. 3, 683-689.
%H A380269 O. T. O’Meara, <a href="https://doi.org/10.1007/978-3-662-41922-9">Introduction to Quadratic Forms</a>, Springer-Verlag Berlin Heidelberg, 1973.
%e A380269 If n <= 5, then the diagonal lattice I_{n+3} is an n-universal Z-lattice of minimal rank, thus a(n) = n+3 for all n <= 5.
%Y A380269 Cf. A054911.
%K A380269 nonn,hard,more
%O A380269 1,1
%A A380269 _Robin Visser_, Jan 18 2025