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 A384428 #36 Jun 30 2025 17:10:59 %S A384428 1,0,4,2,7,0,10,5,3,0,16,4,19,0,6,4,25,0,28,6,9,0,34,5,5,0,6,9,43,0, %T A384428 46,6,15,0,8,5,55,0,18,6,61,0,64,15,8,0,70,6,7,0 %N A384428 a(n) is the minimal area of a polyomino without holes having a product of edge lengths equal to n, or 0 if no solution is possible. %C A384428 Good sequence for elementary school students learning multiplication. %C A384428 If p is the largest prime factor dividing n, then a(n) >= p because there needs to be at least one edge of length k*p for some k>=1. %C A384428 a(51) > 21. - _Sean A. Irvine_, Jun 13 2025 %H A384428 Sean A. Irvine, <a href="https://github.com/archmageirvine/joeis/blob/master/src/irvine/oeis/a384/A384428.java">Java program</a> (github) %F A384428 a(4*n+2) = 0. %F A384428 a(p) = p + (p-1)/2 for any odd prime p. %F A384428 a(p^2) = p for any prime p. %e A384428 a(36)=5 because the V pentomino is the smallest polyomino whose edges multiply together to give 36. The edges of the V pentomino are: 3,3,2,2,1,1. %e A384428 XXX %e A384428 X %e A384428 X %e A384428 a(45)=8 because of the following polyomino with edges 5,3,3,1,1,1,1,1. %e A384428 XXXXX %e A384428 XX %e A384428 X %Y A384428 Cf. A000104, A027709. %K A384428 nonn,more %O A384428 1,3 %A A384428 _Gordon Hamilton_, May 28 2025 %E A384428 a(33)-a(50) from _Sean A. Irvine_, Jun 13 2025