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%I #10 Feb 23 2021 08:30:05
%S 2,3,4,5,3,6,7,4,8,9,5,10,11,4,6,12,13,7,14,5,15,8,16,17,6,9,18,19,5,
%T 10,20,7,21,11,22,23,6,8,12,24,25,13,26,9,27,7,14,28,29,6,10,15,30,31,
%U 8,16,32,11,33,17,34,7,35,9,12,18,36,37,19,38,13,39
%N Irregular triangle read by rows giving the strictly superior divisors of n.
%C We define a divisor d|n to be strictly superior if d > n/d. Strictly superior divisors are counted by A056924.
%e Row n = 18 lists the strictly superior divisors of 18, which are 6, 9, 18.
%e Triangle begins:
%e 1: {}
%e 2: 2
%e 3: 3
%e 4: 4
%e 5: 5
%e 6: 3,6
%e 7: 7
%e 8: 4,8
%e 9: 9
%e 10: 5,10
%e 11: 11
%e 12: 4,6,12
%e 13: 13
%e 14: 7,14
%e 15: 5,15
%e 16: 8,16
%e 17: 17
%e 18: 6,9,18
%e 19: 19
%e 20: 5,10,20
%t Table[Select[Divisors[n],#>n/#&],{n,100}]
%Y Final terms in each row (except n = 1) are A000027.
%Y Row lengths are A056924 (number of strictly superior divisors).
%Y Initial terms in each row are A140271.
%Y The weakly inferior version is A161906.
%Y The weakly superior version is A161908.
%Y Row sums are A238535.
%Y The odd terms in each row are counted by A341594.
%Y The squarefree terms in each row are counted by A341595.
%Y The prime terms in each row are counted by A341642.
%Y The strictly inferior version is A341674.
%Y A001221 counts prime divisors, with sum A001414.
%Y A038548 counts superior (or inferior) divisors.
%Y A207375 list central divisors.
%Y - Inferior: A033676, A063962, A066839, A069288, A217581, A333749, A333750.
%Y - Superior: A033677, A051283, A059172, A063538, A063539, A070038, A072500, A116882, A116883, A341591, A341592, A341593, A341675, A341676.
%Y - Strictly Inferior: A060775, A070039, A333805, A333806, A341596, A341677.
%Y - Strictly Superior: A048098, A064052, A341643, A341644, A341646.
%Y Cf. A000005, A000203, A001222, A001248, A006530, A020639.
%K nonn,tabf
%O 1,1
%A _Gus Wiseman_, Feb 22 2021
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