|
|
A217285
|
|
Irregular triangle read by rows: T(n,k) is the number of labeled relations on n nodes with exactly k edges; n>=0, 0<=k<=n^2.
|
|
2
|
|
|
1, 1, 1, 1, 4, 6, 4, 1, 1, 9, 36, 84, 126, 126, 84, 36, 9, 1, 1, 16, 120, 560, 1820, 4368, 8008, 11440, 12870, 11440, 8008, 4368, 1820, 560, 120, 16, 1, 1, 25, 300, 2300, 12650, 53130, 177100, 480700, 1081575, 2042975, 3268760, 4457400, 5200300, 5200300, 4457400, 3268760, 2042975, 1081575, 480700, 177100, 53130, 12650, 2300, 300, 25, 1
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
0,5
|
|
COMMENTS
|
A labeled relation on 6 nodes will be connected with probability > 99%. It will have at least 10 and no more than 26 edges with probability > 99%.
A random labeled relation can be generated in Mathematica:
GraphPlot[g=Table[RandomInteger[],{6},{6}], DirectedEdges->True, VertexLabeling->True, SelfLoopStyle->True, MultiedgeStyle->True]
|
|
LINKS
|
|
|
FORMULA
|
T(n,k) = binomial(n^2,k).
G.f.: A(x,y) = Sum_{n>=0} x^n*(1+y)^n*Product_{k=1..n} (1-x*(1+y)^(4*k-3))/(1-x*(1+y)^(4*k-1)) due to a q-series identity. - Paul D. Hanna, Aug 22 2013
G.f.: A(x,y) = 1/(1- q*x/(1- (q^3-q)*x/(1- q^5*x/(1- (q^7-q^3)*x/(1- q^9*x/(1- (q^11-q^5)*x/(1- q^13*x/(1- (q^15-q^7)*x/(1- ...))))))))), a continued fraction where q = (1+y), due to an identity of a partial elliptic theta function. - Paul D. Hanna, Aug 22 2013
|
|
EXAMPLE
|
G.f.: A(x,y) = 1 + x*(1+y) + x^2*(1+y)^4 + x^3*(1+y)^9 + x^4*(1+y)^16 +...
Triangle T(n,k) begins:
1;
1, 1;
1, 4, 6, 4, 1;
1, 9, 36, 84, 126, 126, 84, 36, 9, 1;
1, 16, 120, 560, 1820, 4368, 8008, 11440, 12870, 11440, ...
|
|
MATHEMATICA
|
Table[Table[Binomial[n^2, k], {k, 0, n^2}], {n, 0, 6}] //Grid
|
|
PROG
|
(PARI) {T(n, k)=polcoeff((1+x+x*O(x^k))^(n^2), k)}
for(n=0, 6, for(k=0, n^2, print1(T(n, k), ", ")); print("")) \\ Paul D. Hanna, Aug 22 2013
(PARI) {T(n, k)=polcoeff(polcoeff(sum(m=0, n, x^m*(1+y)^m*prod(k=1, m, (1-x*(1+y)^(4*k-3))/(1-x*(1+y)^(4*k-1) +x*O(x^n)))), n, x), k, y)}
{for(n=0, 6, for(k=0, n^2, print1(T(n, k), ", ")); print(""))} \\ Paul D. Hanna, Aug 22 2013
|
|
CROSSREFS
|
|
|
KEYWORD
|
nonn,tabf
|
|
AUTHOR
|
|
|
STATUS
|
approved
|
|
|
|