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 A030247 Number of nonisomorphic idempotent groupoids. 4
 1, 1, 3, 138, 700688, 794734575200, 307047114275109035760, 61899500454067972015948863454485, 9279375475116928325576506574232168143663715776 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 LINKS FORMULA For a list n(1), n(2), n(3), ..., let fixF[n] = prod{i, j >= 1}(sum{d|[ i, j ]}(d*n(d))^((i, j)*n(i)*n(j)-(i=j)n(i))). a(n) = sum {1*s_1+2*s_2+...=n} (fix A[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} (sum {d|i} (d*s_d))^(i*s_i^2-s_i) or {i != j} (sum {d|lcm(i, j)} (d*s_d))^(2*gcd(i, j)*s_i*s_j) a(n) asymptotic to (n^(n^2-n))/n! = A090588(n)/A000142(n) CROSSREFS Cf. A001329, A038015, A038018, A090588. Sequence in context: A336202 A231904 A049677 * A139956 A236193 A070322 Adjacent sequences:  A030244 A030245 A030246 * A030248 A030249 A030250 KEYWORD nonn AUTHOR Christian G. Bower, Feb 15 1998, May 15 1998 and Dec 03 2003 STATUS approved

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Last modified June 25 08:25 EDT 2022. Contains 354835 sequences. (Running on oeis4.)