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Number of strict integer compositions of n whose leaders of increasing runs are increasing.
2

%I #13 Sep 18 2024 20:23:10

%S 1,1,1,2,2,3,5,6,8,11,18,21,30,38,52,77,96,126,167,217,278,402,488,

%T 647,822,1073,1340,1747,2324,2890,3695,4690,5924,7469,9407,11718,

%U 15405,18794,23777,29507,37188,45720,57404,70358,87596,110672,135329,167018,206761,254200,311920

%N Number of strict integer compositions of n whose leaders of increasing runs are increasing.

%C The leaders of increasing runs of a sequence are obtained by splitting it into maximal increasing subsequences and taking the first term of each.

%H Andrew Howroyd, <a href="/A376263/b376263.txt">Table of n, a(n) for n = 0..1000</a>

%H Gus Wiseman, <a href="/A374629/a374629.txt">Sequences counting and ranking compositions by their leaders (for six types of runs)</a>.

%F a(n) = Sum_{k>=1} A008289(n,k)*A000110(k-1) for n > 0. - _Andrew Howroyd_, Sep 18 2024

%e The a(1) = 1 through a(9) = 11 compositions:

%e (1) (2) (3) (4) (5) (6) (7) (8) (9)

%e (1,2) (1,3) (1,4) (1,5) (1,6) (1,7) (1,8)

%e (2,3) (2,4) (2,5) (2,6) (2,7)

%e (1,2,3) (3,4) (3,5) (3,6)

%e (1,3,2) (1,2,4) (1,2,5) (4,5)

%e (1,4,2) (1,3,4) (1,2,6)

%e (1,4,3) (1,3,5)

%e (1,5,2) (1,5,3)

%e (1,6,2)

%e (2,3,4)

%e (2,4,3)

%t Table[Length[Select[Join@@Permutations/@IntegerPartitions[n], UnsameQ@@#&&Less@@First/@Split[#,Less]&]],{n,0,15}]

%o (PARI) \\ here Q(n) gives n-th row of A008289.

%o Q(n)={Vecrev(polcoef(prod(k=1, n, 1 + y*x^k, 1 + O(x*x^n)), n)/y)}

%o a(n)={if(n==0, 1, my(r=Q(n), s=Vec(serlaplace(exp(exp(x+O(x^#r))- 1)))); sum(k=1, #r, r[k]*s[k]))} \\ _Andrew Howroyd_, Sep 18 2024

%Y For less-greater or greater-less we have A294617.

%Y This is a strict case of A374688, weak version A374635.

%Y The strict less-greater version is A374689, weak version A189076.

%Y A003242 counts anti-run compositions, ranks A333489.

%Y A011782 counts compositions, strict A032020.

%Y A238130, A238279, A333755 count compositions by number of runs.

%Y A373949 counts compositions by run-compressed sum, opposite A373951.

%Y A374700 counts compositions by sum of leaders of strictly increasing runs.

%Y Cf. A000110, A008289, A056823, A106356, A188920, A238343, A261982, A274174, A333213, A374634, A374683, A374698, A374763.

%K nonn

%O 0,4

%A _Gus Wiseman_, Sep 18 2024

%E a(26) onwards from _Andrew Howroyd_, Sep 18 2024