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# Bruck-Ryser-Chowla Theorem

If , and the squarefree part of is divisible by a prime , then no difference set of order exists. Equivalently, if a projective plane of order exists, and or 2 (mod 4), then is the sum of two squares.

Dinitz and Stinson (1992) give the theorem in the following form. If a symmetric -block design exists, then

1. If is even, then is a square number,

2. If is odd, then the Diophantine equation

has a solution in integers, not all of which are 0.

## See also

Block Design, Difference Set, Fisher's Block Design Inequality

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## References

Dinitz, J. H. and Stinson, D. R. "A Brief Introduction to Design Theory." Ch. 1 in Contemporary Design Theory: A Collection of Surveys (Ed. J. H. Dinitz and D. R. Stinson). New York: Wiley, pp. 1-12, 1992.Gordon, D. M. "The Prime Power Conjecture is True for ." Electronic J. Combinatorics 1, No. 1, R6, 1-7, 1994. http://www.combinatorics.org/Volume_1/Abstracts/v1i1r6.html.Ryser, H. J. Combinatorial Mathematics. Buffalo, NY: Math. Assoc. Amer., 1963.

## Referenced on Wolfram|Alpha

Bruck-Ryser-Chowla Theorem

## Cite this as:

Weisstein, Eric W. "Bruck-Ryser-Chowla Theorem." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/Bruck-Ryser-ChowlaTheorem.html