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.

A342083 Number of chains of strictly inferior divisors from n to 1.

This page as a plain text file.
%I A342083 #22 Nov 02 2024 09:14:00
%S A342083 1,1,1,1,1,2,1,2,1,2,1,3,1,2,2,2,1,3,1,3,2,2,1,4,1,2,2,3,1,4,1,3,2,2,
%T A342083 2,4,1,2,2,4,1,5,1,3,3,2,1,6,1,3,2,3,1,5,2,4,2,2,1,7,1,2,3,3,2,5,1,3,
%U A342083 2,4,1,8,1,2,3,3,2,5,1,6,2,2,1,7,2,2,2
%N A342083 Number of chains of strictly inferior divisors from n to 1.
%C A342083 We define a divisor d|n to be strictly inferior if d < n/d. Strictly inferior divisors are counted by A056924 and listed by A341674.
%C A342083 These chains have first-quotients (in analogy with first-differences) that are term-wise > their decapitation (maximum element removed). Equivalently, x > y^2 for all adjacent x, y. For example, the divisor chain q = 60/6/2/1 has first-quotients (10,3,2), which are > (6,2,1), so q is counted under a(60).
%C A342083 Also the number of factorizations of n where each factor is greater than the product of all previous factors.
%H A342083 Amiram Eldar, <a href="/A342083/b342083.txt">Table of n, a(n) for n = 1..10000</a>
%F A342083 G.f.: x + Sum_{k>=1} a(k) * x^(k*(k + 1)) / (1 - x^k). - _Ilya Gutkovskiy_, Nov 03 2021
%e A342083 The a(n) chains for n = 2, 6, 12, 24, 42, 48, 60, 72:
%e A342083   2/1  6/1    12/1    24/1    42/1      48/1      60/1      72/1
%e A342083        6/2/1  12/2/1  24/2/1  42/2/1    48/2/1    60/2/1    72/2/1
%e A342083               12/3/1  24/3/1  42/3/1    48/3/1    60/3/1    72/3/1
%e A342083                       24/4/1  42/6/1    48/4/1    60/4/1    72/4/1
%e A342083                               42/6/2/1  48/6/1    60/5/1    72/6/1
%e A342083                                         48/6/2/1  60/6/1    72/8/1
%e A342083                                                   60/6/2/1  72/6/2/1
%e A342083                                                             72/8/2/1
%e A342083 The a(n) factorizations for n = 2, 6, 12, 24, 42, 48, 60, 72:
%e A342083   2  6    12   24    42     48     60      72
%e A342083      2*3  2*6  3*8   6*7    6*8    2*30    8*9
%e A342083           3*4  4*6   2*21   2*24   3*20    2*36
%e A342083                2*12  3*14   3*16   4*15    3*24
%e A342083                      2*3*7  4*12   5*12    4*18
%e A342083                             2*3*8  6*10    6*12
%e A342083                                    2*3*10  2*4*9
%e A342083                                            2*3*12
%t A342083 cen[n_]:=If[n==1,{{1}},Prepend[#,n]&/@Join@@cen/@Select[Divisors[n],#<n/#&]];
%t A342083 Table[Length[cen[n]],{n,100}]
%Y A342083 The restriction to powers of 2 is A040039.
%Y A342083 Not requiring strict inferiority gives A074206 (ordered factorizations).
%Y A342083 The weakly inferior version is A337135.
%Y A342083 The strictly superior version is A342084.
%Y A342083 The weakly superior version is A342085.
%Y A342083 The additive version is A342098, or A000929 allowing equality.
%Y A342083 A000005 counts divisors.
%Y A342083 A001055 counts factorizations.
%Y A342083 A003238 counts chains of divisors summing to n-1, with strict case A122651.
%Y A342083 A038548 counts inferior (or superior) divisors.
%Y A342083 A056924 counts strictly inferior (or strictly superior) divisors.
%Y A342083 A067824 counts strict chains of divisors starting with n.
%Y A342083 A167865 counts strict chains of divisors > 1 summing to n.
%Y A342083 A207375 lists central divisors.
%Y A342083 A253249 counts strict chains of divisors.
%Y A342083 A334996 counts ordered factorizations by product and length.
%Y A342083 A334997 counts chains of divisors of n by length.
%Y A342083 A342086 counts chains of divisors with strictly increasing quotients > 1.
%Y A342083 - Inferior: A033676, A066839, A072499, A161906.
%Y A342083 - Superior: A033677, A070038, A161908.
%Y A342083 - Strictly Inferior: A060775, A070039, A333806, A341674.
%Y A342083 - Strictly Superior: A048098, A064052, A140271, A238535, A341673.
%Y A342083 Cf. A000203, A001248, A002033, A006530, A018819, A020639, A045690, A337105, A342087, A342094, A342095, A342096, A342097.
%K A342083 nonn
%O A342083 1,6
%A A342083 _Gus Wiseman_, Feb 28 2021