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.

A030247 Number of nonisomorphic idempotent groupoids.

Original entry on oeis.org

1, 1, 3, 138, 700688, 794734575200, 307047114275109035760, 61899500454067972015948863454485, 9279375475116928325576506574232168143663715776
Offset: 0

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Author

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

Keywords

Crossrefs

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)

A030250 Number of nonisomorphic groupoids with no idempotents.

Original entry on oeis.org

1, 0, 3, 978, 56630832, 813802235250650, 4797611106478930201025520, 17327898558894838031017212608777367670, 53493753018329066207577438898229132113128344235601408
Offset: 0

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Author

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

Keywords

Crossrefs

A038020 Triangle: T(n,k), k<=n: groupoids with a nontrivial symmetry with n elements and k idempotents.

Original entry on oeis.org

0, 0, 0, 2, 0, 2, 9, 54, 0, 30, 15376, 12664, 14304, 4096, 3187
Offset: 0

Views

Author

Christian G. Bower, May 15 1998

Keywords

Examples

			Triangle begins:
    0;
    0,     0;
    2,     0,     2;
    9,    54,     0,   30;
15376, 12664, 14304, 4096, 3187;
  ...
		

Crossrefs

Row sums are A030246.
Main diagonal is A030249.
Columns k=0..1 are A030252, A030254.

Formula

Difference of A038018 and A038019.
Showing 1-3 of 3 results.