cp's OEIS Frontend

A337484 Number of ordered triples of positive integers summing to n that are neither strictly increasing nor strictly decreasing.

%I A337484 #18 Sep 17 2020 20:34:39
%S A337484 0,0,0,1,3,6,8,13,17,22,28,35,41,50,58,67,77,88,98,111,123,136,150,
%T A337484 165,179,196,212,229,247,266,284,305,325,346,368,391,413,438,462,487,
%U A337484 513,540,566,595,623,652,682,713,743,776,808,841,875,910,944,981,1017
%N A337484 Number of ordered triples of positive integers summing to n that are neither strictly increasing nor strictly decreasing.
%F A337484 a(n) = 2*A242771(n - 1) - A000217(n - 1), n > 0.
%F A337484 2*A001399(n - 6) = 2*A069905(n - 3) = 2*A211540(n - 1) is the complement.
%F A337484 4*A001399(n - 6) = 4*A069905(n - 3) = 4*A211540(n - 1) is the strict case.
%F A337484 Conjectures from _Colin Barker_, Sep 13 2020: (Start)
%F A337484 G.f.: x^3*(1 + 2*x + 2*x^2 - x^3) / ((1 - x)^3*(1 + x)*(1 + x + x^2)).
%F A337484 a(n) = a(n-1) + a(n-2) - a(n-4) - a(n-5) + a(n-6) for n>6.
%F A337484 (End)
%e A337484 The a(3) = 1 through a(7) = 13 triples:
%e A337484   (1,1,1)  (1,1,2)  (1,1,3)  (1,1,4)  (1,1,5)
%e A337484            (1,2,1)  (1,2,2)  (1,3,2)  (1,3,3)
%e A337484            (2,1,1)  (1,3,1)  (1,4,1)  (1,4,2)
%e A337484                     (2,1,2)  (2,1,3)  (1,5,1)
%e A337484                     (2,2,1)  (2,2,2)  (2,1,4)
%e A337484                     (3,1,1)  (2,3,1)  (2,2,3)
%e A337484                              (3,1,2)  (2,3,2)
%e A337484                              (4,1,1)  (2,4,1)
%e A337484                                       (3,1,3)
%e A337484                                       (3,2,2)
%e A337484                                       (3,3,1)
%e A337484                                       (4,1,2)
%e A337484                                       (5,1,1)
%t A337484 Table[Length[Select[Join@@Permutations/@IntegerPartitions[n,{3}],!Less@@#&&!Greater@@#&]],{n,0,15}]
%Y A337484 A140106 is the unordered case.
%Y A337484 A242771 allows strictly increasing but not strictly decreasing triples.
%Y A337484 A337481 counts these compositions of any length.
%Y A337484 A001399(n - 6) counts unordered strict triples.
%Y A337484 A001523 counts unimodal compositions, with complement A115981.
%Y A337484 A007318 and A097805 count compositions by length.
%Y A337484 A069905 counts unordered triples.
%Y A337484 A218004 counts strictly increasing or weakly decreasing compositions.
%Y A337484 A332745 counts partitions with weakly increasing or weakly decreasing run-lengths.
%Y A337484 A332835 counts compositions with weakly increasing or weakly decreasing run-lengths.
%Y A337484 A337483 counts triples either weakly increasing or weakly decreasing.
%Y A337484 Cf. A000212, A000217, A001840, A014311, A046691, A128422, A156040, A332834, A337461, A337482, A337561, A337603, A337604.
%K A337484 nonn
%O A337484 0,5
%A A337484 _Gus Wiseman_, Sep 11 2020