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 A006366 Number of cyclically symmetric plane partitions in the n-cube; also number of 2n X 2n half-turn symmetric alternating sign matrices divided by number of n X n alternating sign matrices. (Formerly M1529) 6
 1, 2, 5, 20, 132, 1452, 26741, 826540, 42939620, 3752922788, 552176360205, 136830327773400, 57125602787130000, 40191587143536420000, 47663133295107416936400, 95288872904963020131203520, 321195665986577042490185260608 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS In the 1995 Encyclopedia of Integer Sequences this sequence appears twice, as both M1529 and M1530. REFERENCES D. M. Bressoud, Proofs and Confirmations, Camb. Univ. Press, 1999; Eq. (6.7) on page 198, except the formula given is incorrect. It should be as shown here. N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence). R. P. Stanley, A baker's dozen of conjectures concerning plane partitions, pp. 285-293 of "Combinatoire Enumerative (Montreal 1985)", Lect. Notes Math. 1234, 1986. LINKS Vincenzo Librandi, Table of n, a(n) for n = 0..90 G. E. Andrews,Plane partitions (III): the Weak Macdonald Conjecture, Invent. Math., 53 (1979), 193-225. P. Di Francesco, P. Zinn-Justin and J.-B. Zuber, Determinant Formulae for some Tiling Problems and Application to Fully Packed Loops, arXiv:math-ph/0410002, 2004. G. Kuperberg, Symmetry classes of alternating-sign matrices under one roof, arXiv:math/0008184 [math.CO], 2000-2001. W. F. Lunnon, The Pascal matrix, Fib. Quart. vol. 15 (1977) pp. 201-204. R. P. Stanley, A baker's dozen of conjectures concerning plane partitions, pp. 285-293 of "Combinatoire Enumerative (Montreal 1985)", Lect. Notes Math. 1234, 1986. Preprint. [Annotated scanned copy] P. J. Taylor, Counting distinct dimer hex tilings, Preprint, 2015. FORMULA a(n) = Product_{i=1..n} (((3*i-1)/(3*i-2))*Product_{j=i..n} (n+i+j-1)/(2*i+j-1)). a(n) ~ exp(1/36) * GAMMA(1/3)^(4/3) * n^(7/36) * 3^(3*n^2/2 + 11/36) / (A^(1/3) * Pi^(2/3) * 2^(2*n^2 + 7/12)), where A = A074962 = 1.2824271291... is the Glaisher-Kinkelin constant. - Vaclav Kotesovec, Mar 01 2015 MAPLE A006366 := proc(n) local i, j; mul((3*i - 1)*mul((n + i + j - 1)/(2*i + j - 1), j = i .. n)/(3*i - 2), i = 1 .. n) end; MATHEMATICA Table[Product[(3i-1)/(3i-2) Product[(n+i+j-1)/(2i+j-1), {j, i, n}], {i, n}], {n, 0, 20}] (* Harvey P. Dale, Apr 17 2013 *) PROG (PARI) a(n)=prod(i=0, n-1, (3*i+2)*(3*i)!/(n+i)!) CROSSREFS Cf. A005130, also A003827, A005156, A005158, A005160-A005164, A048601, A050204. Sequence in context: A076795 A130293 A156073 * A012317 A297630 A297629 Adjacent sequences:  A006363 A006364 A006365 * A006367 A006368 A006369 KEYWORD nonn,nice,easy AUTHOR STATUS approved

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Last modified June 2 14:21 EDT 2020. Contains 334787 sequences. (Running on oeis4.)