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 A079190 Number of isomorphism classes of anti-commutative closed binary operations (groupoids) on a set of order n. 6
 1, 6, 996, 31857648, 266666713602640, 929809173755713574913480, 2002123402266181527640478418179038176, 3702236248557739850415303240942330019881771301360640 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS A079187(n)+A079190(n)=A001329(n). Each a(n) is equal to the sum of the elements in row n of A079191. LINKS C. van den Bosch, Closed binary operations on small sets FORMULA a(n) = sum {1*s_1+2*s_2+...=n} (fixA[s_1, s_2, ...]/(1^s_1*s_1!*2^s_2*s2!*...)) where fixA[s_1, s_2, ...] = prod {i>=j>=1} f(i, j, s_i, s_j) where f(i, j, s_i, s_j) = {i=j, odd} (sum {d|i} (d*s_d))^(s_i*(i*s_i+1)/2) * (-1 + sum {d|i} (d*s_d))^(s_i*(i*s_i-1)/2) or {i=j, even} (sum {d|i and d/i is odd} (d*s_d))^s_i * (sum {d|i} (d*s_d))^(i*s_i^2/2) * (-1 + sum {d|i} (d*s_d))^(s_i*(i*s_i-2)/2) or {i < j} (sum {d|lcm(i, j)} (d*s_d))^(gcd(i, j)*s_i*s_j) or {i > j} (-1 + sum {d|lcm(i, j)} (d*s_d))^(gcd(i, j)*s_i*s_j) a(n) is asymptotic to (n^binomial(n+1, 2) * (n-1)^binomial(n, 2))/n! = A079189(n)/A000142(n) CROSSREFS Cf. A079187, A079189, A079191. Sequence in context: A332196 A024085 A080474 * A203303 A159865 A004806 Adjacent sequences: A079187 A079188 A079189 * A079191 A079192 A079193 KEYWORD nonn AUTHOR Christian van den Bosch (cjb(AT)cjb.ie), Jan 03 2003 EXTENSIONS Edited, corrected and extended with formula by Christian G. Bower, Dec 12 2003 STATUS approved

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Last modified March 24 14:39 EDT 2023. Contains 361479 sequences. (Running on oeis4.)