A228360 Table read by antidiagonals: T(l,L) is the number of all possible covers of L-length line segment by l-length line segments with allowed gaps < l.

0, 1, 0, 1, 0, 0, 1, 1, 0, 0, 1, 2, 0, 0, 0, 1, 2, 1, 0, 0, 0, 1, 3, 2, 0, 0, 0, 0, 1, 4, 3, 1, 0, 0, 0, 0, 1, 5, 3, 2, 0, 0, 0, 0, 0, 1, 7, 4, 3, 1, 0, 0, 0, 0, 0, 1, 9, 6, 4, 2, 0, 0, 0, 0, 0, 0, 1, 12, 8, 4, 3, 1, 0, 0, 0, 0, 0, 0

Offset

1,12

Comments

Second row is A228361 which also corresponds to Padovan's spiral numbers A134816 for n>1.

Third row is A228362.

T(l,L) is also the number of compositions of L where parts do not exceeds l and where are no two adjacent parts less than l.

T(2,5) = 3: [2,2,1], [2,1,2], [1,2,2]

T(2,9) = 9: [2,2,2,2,1], [2,2,2,1,2], [2,2,1,2,2], [2,1,2,2,2], [1,2,2,2,2], [2,1,2,1,2,1], [1,2,2,1,2,1], [1,2,1,2,2,1], [1,2,1,2,1,2]

T(3,8) = 6: [3,3,2], [3,1,3,1], [3,2,3], [1,3,3,1], [1,3,1,3], [2,3,3]

Links

Table of n, a(n) for n=1..78.

Formula

For all l>=1:

G.f.: (1 - Sum[x^i, {i, l, 2 l - 1}])^-1*Sum[x^i, {i, 0, l - 1}]^2*x^l.

G.f. for l=1: x/(1-x).

G.f. for l=2: x^2*(1+x)^2/(1-x^2-x^3).

G.f. for l=3: x^3*(1 + x + x^2)^2/(1 - x^3 - x^4 - x^5).

For l>1, L>=0:

c[k, l, m] = Sum[(-1)^i binomial[k - 1 - i*l, m - 1] binomial[m, i], {i, 0, floor[(k - m)/l]}] // number of compositions of k into exactly m parts which do not exceed l.

a[L, l, m] = Sum[ binomial[m + 1, m + 1 - j]*c[L - l*m, l - 1, j], {j, 0, m + 1}] //the number of all possible covers of L-length line segment by m l-length line segments.

T[l, L] := Sum[a[L, l, j], {j, 1, ceiling[L/l]}].

Example

Table starts:
0, 1, 1, 1, 1, 1, 1, 1, 1, 1,  1,  1,  1,  1,  1, ...
0, 0, 1, 2, 2, 3, 4, 5, 7, 9, 12, 16, 21, 28, 37, ...
0, 0, 0, 1, 2, 3, 3, 4, 6, 8, 10, 13, 18, 24, 31, ...
0, 0, 0, 0, 1, 2, 3, 4, 4, 5,  7, 10, 13, 16, 20, ...
0, 0, 0, 0, 0, 1, 2, 3, 4, 5,  5,  6,  8, 11, 15, ...
0, 0, 0, 0, 0, 0, 1, 2, 3, 4,  5,  6,  6,  7,  9, ...
0, 0, 0, 0, 0, 0, 0, 1, 2, 3,  4,  5,  6,  7,  7, ...
0, 0, 0, 0, 0, 0, 0, 0, 1, 2,  3,  4,  5,  6,  7, ...
0, 0, 0, 0, 0, 0, 0, 0, 0, 1,  2,  3,  4,  5,  6, ...
0, 0, 0, 0, 0, 0, 0, 0, 0, 0,  1,  2,  3,  4,  5, ...
0, 0, 0, 0, 0, 0, 0, 0, 0, 0,  0,  1,  2,  3,  4, ...
0, 0, 0, 0, 0, 0, 0, 0, 0, 0,  0,  0,  1,  2,  3, ...
0, 0, 0, 0, 0, 0, 0, 0, 0, 0,  0,  0,  0,  1,  2, ...
0, 0, 0, 0, 0, 0, 0, 0, 0, 0,  0,  0,  0,  0,  1, ...
.....................................................

Mathematica

Gf[l_, z] := (1 - Sum[z^i, {i, l, 2 l - 1}])^-1*Sum[z^i, {i, 0, l - 1}]^2*z^l
T[l_, L_] := CoefficientList[Series[Gf[l, z], {z, 0, 100}], z][[L + 1]]
Table[T[n - b + 1, b - 1], {n, 1, 30}, {b, n, 1, -1}] // Flatten

Crossrefs

Sequence in context: A325336 A060016 A117408 * A303138 A276205 A244966

Adjacent sequences: A228357 A228358 A228359 * A228361 A228362 A228363

Keyword

nonn,tabl

Author

Philipp O. Tsvetkov, Aug 21 2013

Status

approved