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 A263232 Triangle read by rows: T(n,k) is the number of partitions of n having exactly k parts equal to 3 (n >= 0, 0 <= k <= floor(n/3)). 3

%I

%S 1,1,2,2,1,4,1,5,2,8,2,1,10,4,1,15,5,2,19,8,2,1,27,10,4,1,34,15,5,2,

%T 47,19,8,2,1,59,27,10,4,1,79,34,15,5,2,99,47,19,8,2,1,130,59,27,10,4,

%U 1,162,79,34,15,5,2,209,99,47,19,8,2,1,259,130,59,27,10,4,1

%N Triangle read by rows: T(n,k) is the number of partitions of n having exactly k parts equal to 3 (n >= 0, 0 <= k <= floor(n/3)).

%C Row n has 1+floor(n/3) terms. Row sums are the partition numbers (A000041). T(n,0) = A027337(n). Sum_{k=0..floor(n/3)} k*T(n,k) = A024787(n).

%H Alois P. Heinz, <a href="/A263232/b263232.txt">Rows n = 0..300, flattened</a>

%F G.f.: (1-x)*(1-x^2)*(1-tx^3)*Product_{j>=4} (1-x^j).

%e T(7,1) = 4 because we have [4,3], [3,2,2], [3,2,1,1], and [3,1,1,1,1].

%e T(9,2) = 2 because we have [3,3,2,1] and [3,3,1,1,1].

%e Triangle starts:

%e 1;

%e 1;

%e 2;

%e 2, 1;

%e 4, 1;

%e 5, 2;

%e 8, 2, 1.

%p g := 1/((1-x)*(1-x^2)*(1-t*x^3)*(product(1-x^j, j = 4 .. 80))): gser := simplify(series(g, x = 0, 30)): for n from 0 to 25 do P[n] := sort(coeff(gser, x, n)) end do: for n from 0 to 25 do seq(coeff(P[n], t, j), j = 0 .. floor((1/3)*n)) end do; # yields sequence in triangular form

%p # second Maple program:

%p b:= proc(n, i) option remember; expand(

%p `if`(n=0, 1, `if`(i<1, 0, `if`(i=3, x, 1)*

%p `if`(i>n, 0, b(n-i, i)) +b(n, i-1))))

%p end:

%p T:= n-> (p-> seq(coeff(p, x, i), i=0..degree(p)))(b(n\$2)):

%p seq(T(n), n=0..25); # _Alois P. Heinz_, Nov 01 2015

%t b[n_, i_] := b[n, i] = Expand[If[n == 0, 1, If[i < 1, 0, If[i == 3, x, 1]* If[i > n, 0, b[n - i, i]] + b[n, i - 1]]]]; T[n_] := Function[p, Table[ Coefficient[p, x, i], {i, 0, Exponent[p, x]}]][b[n, n]]; Table[T[n], {n, 0, 25}] // Flatten (* _Jean-François Alcover_, Jan 21 2016, after _Alois P. Heinz_ *)

%Y Cf. A000041, A027337, A024787, A116599.

%K nonn,tabf

%O 0,3

%A _Emeric Deutsch_, Nov 01 2015

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Last modified December 12 01:57 EST 2019. Contains 329948 sequences. (Running on oeis4.)