cp's OEIS Frontend

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.

A342085 Number of decreasing chains of distinct superior divisors starting with n.

This page as a plain text file.
%I A342085 #13 Jun 24 2021 20:13:17
%S A342085 1,1,1,2,1,2,1,3,2,2,1,5,1,2,2,6,1,5,1,4,2,2,1,11,2,2,3,4,1,7,1,10,2,
%T A342085 2,2,15,1,2,2,10,1,6,1,4,5,2,1,26,2,5,2,4,1,11,2,10,2,2,1,21,1,2,5,20,
%U A342085 2,6,1,4,2,7,1,39,1,2,5,4,2,6,1,23,6,2,1
%N A342085 Number of decreasing chains of distinct superior divisors starting with n.
%C A342085 We define a divisor d|n to be superior if d >= n/d. Superior divisors are counted by A038548 and listed by A161908.
%C A342085 These chains have first-quotients (in analogy with first-differences) that are term-wise less than or equal to their decapitation (maximum element removed). Equivalently, x <= y^2 for all adjacent x, y. For example, the divisor chain q = 24/8/4/2 has first-quotients (3,2,2), which are less than or equal to (8,4,2), so q is counted under a(24).
%C A342085 Also the number of ordered factorizations of n where each factor is less than or equal to the product of all previous factors.
%H A342085 Alois P. Heinz, <a href="/A342085/b342085.txt">Table of n, a(n) for n = 1..65536</a>
%F A342085 a(2^n) = A045690(n).
%e A342085 The a(n) chains for n = 2, 4, 8, 12, 16, 20, 24, 30, 32:
%e A342085   2  4    8      12      16        20       24         30       32
%e A342085      4/2  8/4    12/4    16/4      20/5     24/6       30/6     32/8
%e A342085           8/4/2  12/6    16/8      20/10    24/8       30/10    32/16
%e A342085                  12/4/2  16/4/2    20/10/5  24/12      30/15    32/8/4
%e A342085                  12/6/3  16/8/4             24/6/3     30/6/3   32/16/4
%e A342085                          16/8/4/2           24/8/4     30/10/5  32/16/8
%e A342085                                             24/12/4    30/15/5  32/8/4/2
%e A342085                                             24/12/6             32/16/4/2
%e A342085                                             24/8/4/2            32/16/8/4
%e A342085                                             24/12/4/2           32/16/8/4/2
%e A342085                                             24/12/6/3
%e A342085 The a(n) ordered factorizations for n = 2, 4, 8, 12, 16, 20, 24, 30, 32:
%e A342085   2  4    8      12     16       20     24       30     32
%e A342085      2*2  4*2    4*3    4*4      5*4    6*4      6*5    8*4
%e A342085           2*2*2  6*2    8*2      10*2   8*3      10*3   16*2
%e A342085                  2*2*3  2*2*4    5*2*2  12*2     15*2   4*2*4
%e A342085                  3*2*2  4*2*2           3*2*4    3*2*5  4*4*2
%e A342085                         2*2*2*2         4*2*3    5*2*3  8*2*2
%e A342085                                         4*3*2    5*3*2  2*2*2*4
%e A342085                                         6*2*2           2*2*4*2
%e A342085                                         2*2*2*3         4*2*2*2
%e A342085                                         2*2*3*2         2*2*2*2*2
%e A342085                                         3*2*2*2
%p A342085 a:= proc(n) option remember; 1+add(`if`(d>=n/d,
%p A342085       a(d), 0), d=numtheory[divisors](n) minus {n})
%p A342085     end:
%p A342085 seq(a(n), n=1..128);  # _Alois P. Heinz_, Jun 24 2021
%t A342085 cmo[n_]:=Prepend[Prepend[#,n]&/@Join@@cmo/@Select[Most[Divisors[n]],#>=n/#&],{n}];
%t A342085 Table[Length[cmo[n]],{n,100}]
%Y A342085 The restriction to powers of 2 is A045690.
%Y A342085 The inferior version is A337135.
%Y A342085 The strictly inferior version is A342083.
%Y A342085 The strictly superior version is A342084.
%Y A342085 The additive version is A342094, with strict case A342095.
%Y A342085 The additive version not allowing equality is A342098.
%Y A342085 A001055 counts factorizations.
%Y A342085 A003238 counts divisibility chains summing to n-1, with strict case A122651.
%Y A342085 A038548 counts inferior (or superior) divisors.
%Y A342085 A056924 counts strictly inferior (or strictly superior) divisors.
%Y A342085 A067824 counts strict chains of divisors starting with n.
%Y A342085 A074206 counts strict chains of divisors from n to 1 (also ordered factorizations).
%Y A342085 A167865 counts strict chains of divisors > 1 summing to n.
%Y A342085 A207375 lists central divisors.
%Y A342085 A253249 counts strict chains of divisors.
%Y A342085 A334996 counts ordered factorizations by product and length.
%Y A342085 A334997 counts chains of divisors of n by length.
%Y A342085 - Inferior: A033676, A066839, A072499, A161906.
%Y A342085 - Superior: A033677, A070038, A161908, A341676.
%Y A342085 - Strictly Inferior: A060775, A070039, A333806, A341674.
%Y A342085 - Strictly Superior: A064052/A048098, A140271, A238535, A341673.
%Y A342085 Cf. A000203, A001248, A005117, A006530, A020639, A057567, A057568, A112798, A169594, A337105, A342096, A342097.
%K A342085 nonn
%O A342085 1,4
%A A342085 _Gus Wiseman_, Feb 28 2021