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 A090588 Number of labeled idempotent groupoids. 5
 1, 1, 4, 729, 16777216, 95367431640625, 221073919720733357899776, 311973482284542371301330321821976049, 374144419156711147060143317175368453031918731001856, 507528786056415600719754159741696356908742250191663887263627442114881 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 LINKS FORMULA a(n) = n^(n^2 - n). MAPLE a:=n->mul(mul(sum(1, j=0..n), k=0..n), m=1..n): seq(a(n), n=-1..7); # Zerinvary Lajos, Dec 31 2008 MATHEMATICA Join[{1}, Table[n^(n^2-n), {n, 10}]] (* Harvey P. Dale, Sep 16 2013 *) PROG (Ruby) def a(n) ids =* (0..n-1) return (ids.product(ids)).reduce(1){ |accum, x|  (x[0] == x[1]) ? accum :  accum*ids.length} end # Chad Brewbaker, Nov 03 2013 (PARI) a(n) = n^(n^2-n); \\ Joerg Arndt, Nov 04 2013 (MAGMA) [n^(n^2 - n): n in [0..10]]; // Vincenzo Librandi, Aug 08 2015 CROSSREFS Cf. A002489, A030247, A076113. Sequence in context: A219012 A059754 A134579 * A053986 A222961 A160737 Adjacent sequences:  A090585 A090586 A090587 * A090589 A090590 A090591 KEYWORD nonn AUTHOR Christian G. Bower, Dec 03 2003 EXTENSIONS One additional term from Harvey P. Dale, Sep 16 2013 STATUS approved

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Last modified August 12 11:44 EDT 2020. Contains 336439 sequences. (Running on oeis4.)