This site is supported by donations to The OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A266305 Number of n X n symmetric matrices with nonnegative integer entries and without zero rows or columns such that the sum of all entries is equal to 2n. 3
 1, 1, 7, 74, 1060, 19013, 408650, 10219360, 291158230, 9302358947, 329192040880, 12775809098058, 539351216354728, 24600280965461923, 1205263251360664310, 63115789721408960624, 3517483455875467926588, 207834769804597591153769, 12976002600530598793672490 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 LINKS Alois P. Heinz, Table of n, a(n) for n = 0..200 FORMULA a(n) = A138177(2n,n). EXAMPLE a(2) = 7: [1 1]  [2 1]  [0 1]  [2 0]  [0 2]  [3 0]  [1 0] [1 1]  [1 0]  [1 2]  [0 2]  [2 0]  [0 1]  [0 3]. MAPLE gf:= k-> 1/((1-x)^k*(1-x^2)^(k*(k-1)/2)): A:= (n, k)-> coeff(series(gf(k), x, n+1), x, n): a:= n-> add(A(2*n, n-j)*(-1)^j*binomial(n, j), j=0..n): seq(a(n), n=0..20); MATHEMATICA gf[k_] := 1/((1-x)^k*(1-x^2)^(k*(k-1)/2)); A[n_, k_] := SeriesCoefficient[ gf[k], {x, 0, n}]; a[n_] := Sum[A[2*n, n-j]*(-1)^j*Binomial[n, j], {j, 0, n}]; Table[a[n], {n, 0, 20}] (* Jean-François Alcover, Feb 25 2017, translated from Maple *) CROSSREFS Cf. A138177, A268309. Sequence in context: A114472 A000901 A295245 * A098118 A097821 A054745 Adjacent sequences:  A266302 A266303 A266304 * A266306 A266307 A266308 KEYWORD nonn AUTHOR Alois P. Heinz, Jan 31 2016 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified August 24 22:41 EDT 2019. Contains 326314 sequences. (Running on oeis4.)