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 A373723 #16 Apr 21 2025 02:35:04
%S A373723 0,0,22,597,7178,43090,207494,748801,2321973,6267631,15596170,
%T A373723 34784307,74017706,147072570,277965322,503711791,884612799,1491687919,
%U A373723 2458600175,3925566799,6133712065,9388594434,14121653942,20783339478,30178942357,43156537147,60868287839,84699183224,116688767652
%N A373723 Number of strictly totally positive 3 X 3 matrices having all terms in {1,...,n}.
%C A373723 A matrix is strictly totally positive if all its minors are greater than zero.
%H A373723 Robin Visser, <a href="/A373723/b373723.txt">Table of n, a(n) for n = 1..40</a>
%t A373723 ispositive1[M_]:=ispositive1[M]=Union@Table[Select[Union@Flatten@Minors[M,r],(#<= 0)&]=={},{r,1,Length[M]}]=={True}; W[n_]:=W[n]=Flatten[Table[{{a11,a12,a13},{a21,a22,a23},{a31,a32,a33}},{a11,1,n},{a12,1,n},{a13,1,n},{a21,1,n},{a22,1,n},{a23,1,n},{a31,1,n},{a32,1,n},{a33,1,n}],8]; Table[Length@Select[W[n],ispositive1[#]&],{n,1,7}]
%o A373723 (Sage)
%o A373723 import itertools
%o A373723 def a(n):
%o A373723 ans, W = 0, itertools.product(range(1,n+1), repeat=9)
%o A373723 for w in W:
%o A373723 M = Matrix(ZZ, 3, 3, w)
%o A373723 if (min(M.minors(2)) > 0) and (M.det() > 0): ans += 1
%o A373723 return ans # _Robin Visser_, Apr 18 2025
%Y A373723 Cf. A211059, A373724.
%K A373723 nonn
%O A373723 1,3
%A A373723 _José María Grau Ribas_, Jun 15 2024
%E A373723 More terms from _Robin Visser_, Apr 18 2025