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.

A294615 a(n) is the smallest prime p such that there is a multiplicative subgroup H of Z/pZ, of odd order and of index 2n, such that for any two cosets H1 and H2 of H, H1 + H2 contains all of (Z/pZ)\0, except that H+H contains all of (Z/pZ)\0 except -H. If no such prime exists, a(n) = 0.

Original entry on oeis.org

0, 29, 67, 233, 491, 661, 911, 0, 1747, 2861, 2531, 2857, 7307, 4733, 5791, 7457, 9011, 7309, 14327, 11801, 11047, 14741, 67391, 26737, 16451, 14717, 32779, 41609, 24071, 30661
Offset: 1

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Author

Jeremy F. Alm, Nov 04 2017

Keywords

Comments

The fact that H is of odd order means H is disjoint from -H. The finite integral relation algebra with n pairs of asymmetric diversity atoms a_i, where the forbidden cycles are of the form (a_i, a_i, a_i^(converse)), is representable over Z/pZ, where p = a(n). These are "directed anti-Ramsey algebras", since "monochromatic intransitive triangles" are forbidden.

Crossrefs

Cf. A263308.

A294676 Ramsey-Comer numbers: a(n) is the smallest prime p congruent to 1 mod 2n such that for every prime q >= p (also congruent to 1 mod 2n), the multiplicative subgroup H of (Z/qZ)* of index n contains a solution to x+y = z.

Original entry on oeis.org

3, 13, 19, 73, 131, 313, 547, 193, 613, 1201, 1453, 1249, 547, 2857, 2971, 1601, 4217, 3169, 2243, 4441, 9661, 10957, 7039, 7873, 8951, 11701, 14419, 18257, 11311, 29641
Offset: 1

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Author

Jeremy F. Alm, Nov 06 2017

Keywords

Comments

a(n) <= n^4 + 5 (cf. Alm, 2017).
The subgroup H, along with its n-1 cosets, induces a cyclic coloring on K_q. Labeling the vertices 0 through q-1, color the edge uv by the color corresponding to the coset containing u-v (mod q). Thus if q >= a(n), the coloring induced by H and its cosets must contain a monochromatic triangle. In fact, it contains many monochromatic triangles in each color class.
The data gathered thus far suggest that the bound n^4 + 5 can be replaced by cn^3 for some c > 1, but there is no proof.
a(n) > A263308(n). The reason A263308(8) is zero can be taken to be that a(8) is exceptionally small; similarly, a(13) is small, so A263308(13)=0.

Crossrefs

Cf. A263308.

A305464 Largest prime modulus p such that there exists a multiplicative-coset Ramsey algebra in n colors over Z/pZ, or 0 if no such prime exists.

Original entry on oeis.org

5, 13, 41, 101, 277, 491, 0, 577, 1181, 1409, 1201, 0, 2801, 2851, 1217, 4013, 3061, 1901, 4241, 9619, 10781, 6947, 7681, 8501, 11597, 14149, 18089, 10847
Offset: 2

Views

Author

Jeremy F. Alm, Jun 01 2018

Keywords

Comments

a(n) <= n^4 + 5 (cf. Alm, 2017). There cannot be arbitrarily large multiplicative-coset Ramsey algebras in a fixed number of colors.
a(n) < A294676(n).

Crossrefs

Showing 1-3 of 3 results.