|
|
A241619
|
|
T(n,k)=Number of length n+2 0..k arrays with no consecutive three elements summing to more than k
|
|
15
|
|
|
4, 10, 6, 20, 20, 9, 35, 50, 40, 13, 56, 105, 125, 76, 19, 84, 196, 315, 295, 147, 28, 120, 336, 686, 889, 711, 287, 41, 165, 540, 1344, 2254, 2567, 1730, 556, 60, 220, 825, 2430, 5040, 7586, 7483, 4175, 1077, 88, 286, 1210, 4125, 10242, 19374, 25774, 21631, 10077
(list;
table;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
1,1
|
|
COMMENTS
|
Table starts
...4...10....20.....35......56.......84......120.......165.......220........286
...6...20....50....105.....196......336......540.......825......1210.......1716
...9...40...125....315.....686.....1344.....2430......4125......6655......10296
..13...76...295....889....2254.....5040....10242.....19305.....34243......57772
..19..147...711...2567....7586....19374....44274.....92697....180829.....332761
..28..287..1730...7483...25774....75180...193194....449295....963886....1934647
..41..556..4175..21631...86828...289248...835812...2159025...5093737...11151140
..60.1077.10077..62547..292621..1113348..3617703..10380183..26932543...64309245
..88.2091.24377.181255..988303..4294574.15692003..50011289.142701909..371651553
.129.4057.58928.524877.3335451.16553380.68014233.240772037.755538278.2146210209
|
|
LINKS
|
|
|
FORMULA
|
Empirical for column k, apparently a recurrence of order (k+1)*(k+2)/2:
k=1: a(n) = a(n-1) +a(n-3)
k=2: a(n) = a(n-1) +a(n-2) +2*a(n-3) -a(n-5) -a(n-6)
k=3: a(n) = 2*a(n-1) +4*a(n-3) -3*a(n-4) -a(n-5) -3*a(n-6) +2*a(n-7) +a(n-9) -a(n-10)
k=4: [order 15]
k=5: [order 21]
k=6: [order 28]
k=7: [order 36]
k=8: [order 45]
k=9: [order 55]
k=10: [order 66]
k=11: [order 78]
k=12: [order 91]
Empirical for row n, apparently a polynomial of degree n+2:
n=1: a(n) = (1/6)*n^3 + 1*n^2 + (11/6)*n + 1
n=2: a(n) = (1/12)*n^4 + (2/3)*n^3 + (23/12)*n^2 + (7/3)*n + 1
n=3: a(n) = (1/24)*n^5 + (5/12)*n^4 + (13/8)*n^3 + (37/12)*n^2 + (17/6)*n + 1
n=4: [polynomial of degree 6]
n=5: [polynomial of degree 7]
n=6: [polynomial of degree 8]
n=7: [polynomial of degree 9]
Column k satisfies a recurrence of order (k+1)*(k+2)/2, since a(n)=e^T T^n e where T is a (k+1)*(k+2)/2 matrix and e the vector of all 1's (see proofs at A241615 and A241618).
Row n is the Ehrhart polynomial of degree n+2 corresponding to the polytope {(x(1),...,x(n+2)): all x(i)>=0, x(i)+x(i+1)+x(i+2)<=1 for i=1..n}, whose vertices have all entries in {0,1}. (End)
|
|
EXAMPLE
|
Some solutions for n=5 k=4
..1....0....2....1....0....2....0....1....0....0....0....2....1....0....1....2
..0....0....1....3....0....0....4....2....1....0....1....1....3....0....0....1
..0....3....0....0....0....1....0....1....3....0....0....0....0....2....1....0
..0....0....0....1....2....0....0....0....0....0....1....0....1....1....1....2
..2....0....3....0....0....2....0....0....0....0....2....1....0....0....0....0
..0....1....0....1....2....1....2....0....1....0....0....1....1....0....3....1
..0....0....0....1....0....0....2....4....2....2....0....0....2....0....0....0
|
|
MAPLE
|
for m from 1 to 12 do
r:= [seq(seq([i, j], j=0..m-i), i=0..m)];
T[m]:= Matrix((m+1)*(m+2)/2, (m+1)*(m+2)/2, proc(i, j) if r[i][1]=r[j][2] and r[i][1]+r[i][2]+r[j][1]<=m then 1 else 0 fi end proc):
U[m, 0]:= Vector((m+1)*(m+2)/2, 1);
od:
R:= NULL:
for i from 2 to 12 do
for j from 1 to i-1 do
U[i-j, j]:= T[i-j] . U[i-j, j-1];
R:= R, convert(U[i-j, j], `+`)
od od:
|
|
CROSSREFS
|
|
|
KEYWORD
|
|
|
AUTHOR
|
|
|
STATUS
|
approved
|
|
|
|