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 A221704 Let K be a local ring with a principal maximal ideal J of nilpotent degree 4 with |K/J|>2; a(n) = number of D-invariant ideals in the ring R_n(K,J). 2
 20, 96, 440, 1956, 8522, 36616, 155748, 657468, 2759040, 11523584, 47944480, 198834824, 822365998, 3393330152, 13973673788, 57441828332, 235759507928, 966292212992, 3955570350128, 16174269135992, 66069496614548, 269635886185424, 1099484607270920, 4479870682221016, 18240349141736352, 74219083904054016, 301810005706454016 (list; graph; refs; listen; history; text; internal format)
 OFFSET 2,1 REFERENCES G. P. Egorychev et al., Enumeration of ideals of some nilpotent matrix rings, J. Algebra and Applications, 12 (2013), #1250140. LINKS MAPLE f:=(n, s)->(2*s*n-s-3*n+1)*binomial(2*n-2, n-1)-(4/n)*binomial(2*n, n-2)+2^(2*n-1); [seq(f(n, 4), n=2..40)]; PROG (Maxima) A221704(n, s):=(2*s*n-s-3*n+1)*binomial(2*n-2, n-1)-(4/n)*binomial(2*n, n-2)+2^(2*n-1)\$ makelist(A221704(n, 4), n, 2, 40); /* Martin Ettl, Jan 24 2013 */ CROSSREFS Sequence in context: A124948 A126407 A158446 * A222772 A267646 A264424 Adjacent sequences:  A221701 A221702 A221703 * A221705 A221706 A221707 KEYWORD nonn AUTHOR N. J. A. Sloane, Jan 22 2013 STATUS approved

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Last modified August 9 06:47 EDT 2022. Contains 356018 sequences. (Running on oeis4.)