cp's OEIS Frontend

This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

Showing 1-3 of 3 results.

A030257 Number of nonisomorphic commutative idempotent groupoids.

Original entry on oeis.org

1, 1, 1, 7, 192, 82355, 653502972, 110826042515867, 479732982053513924168, 62082231641825701423422054735, 275573192431752191557427399293883120600, 47363301285150007842253190185182901101879369430257
Offset: 0

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Author

Christian G. Bower, Feb 15 1998, May 15 1998 and Dec 03 2003

Keywords

Crossrefs

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, ...] = Product_{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))^((i*s_i^2-s_i)/2) or {i=j, even} (Sum_{d|i} (d*s_d))^((i*s_i^2-2*s_i)/2) * (Sum_{d|i/2} (d*s_d))^s_i or {i != j} (Sum_{d|lcm(i, j)} (d*s_d))^(gcd(i, j)*s_i*s_j). - Corrected by Sean A. Irvine, Mar 27 2020
a(n) is asymptotic to (n^binomial(n-1, 2))/n! = A076113(n)/A000142(n).

A030260 Number of nonisomorphic commutative groupoids with no idempotents.

Original entry on oeis.org

1, 0, 1, 38, 13872, 83360520, 10203847031340, 31023254154131753920, 2765562268014305034000397632, 8332535835277886736134596954072281240, 960864308045670310058158724983067048253497223280
Offset: 0

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Author

Christian G. Bower, Feb 15 1998 and May 15 1998

Keywords

Crossrefs

A038023 Triangle: T(n,k), k<=n: commutative groupoids with a nontrivial symmetry with n elements and k idempotents.

Original entry on oeis.org

0, 0, 0, 0, 0, 0, 3, 6, 0, 4, 96, 214, 128, 64, 38, 54248, 83925, 54223, 28254, 10223, 1894
Offset: 0

Views

Author

Christian G. Bower, May 15 1998

Keywords

Crossrefs

Formula

Difference of A038021 and A038022.
Showing 1-3 of 3 results.