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 A081532 #20 Feb 16 2025 08:32:48 %S A081532 1,1,2,1,2,4,1,2,3,6,1,2,4,8,16,1,2,3,4,6,12,1,2,4,8,16,32,64,1,2,3,4, %T A081532 6,8,12,24,1,2,3,4,6,9,12,18,36,1,2,3,4,6,8,12,16,24,48,1,2,4,8,16,32, %U A081532 64,128,256,512,1024,1,2,3,4,5,6,10,12,15,20,30,60,1,2,4,8,16,32,64,128,256,512,1024,2048,4096 %N A081532 Triangle read by rows: let m be smallest number with n divisors, then row n gives divisors of m. %H A081532 Michel Marcus, <a href="/A081532/b081532.txt">Rows n=1..200 of triangle, flattened</a> %H A081532 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/Divisor.html">Divisor</a> %F A081532 T(n,k) = k-th divisor of smallest number having exactly n divisors, 1<=k<=n. %F A081532 T(n,1) = 1, T(n,n) = A005179(n); A000005(T(n,n)) = n. %e A081532 Triangle begins %e A081532 1; %e A081532 1,2; %e A081532 1,2,4; %e A081532 1,2,3,6; %e A081532 1,2,4,8,16; %e A081532 1,2,3,4,6,12; %e A081532 ... %t A081532 Function[s, Map[Lookup[s, #] &, Range[First@ Complement[Range@ Max@ #, #] - 1]] &@ Keys@ s]@ Map[Divisors@ First@ # &, KeySort@ PositionIndex@ Array[DivisorSigma[0, #] &, 5000]] // Flatten (* _Michael De Vlieger_, Nov 15 2020 *) %Y A081532 Leading diagonal is A005179. Cf. A000005, A081533. %K A081532 nonn,tabl %O A081532 1,3 %A A081532 _Amarnath Murthy_, Mar 28 2003 %E A081532 More terms from _Sam Alexander_, Oct 21 2003 %E A081532 More terms from _Michel Marcus_, Nov 15 2020