Template talk:Number of relations
Surely {} and {(x,x)} are both reflexive binary relations over {x}? (Hence there are 2 reflexive binary relations over a 1-element set.) Hairy Dude 23:07, 14 November 2007 (UTC)
- "Reflexive" means that x must be related to itself. This is true for {(x,x)} but not for {}. —David Eppstein 00:21, 15 November 2007 (UTC)
- Yes. {} is reflexive over {}, but not over {x}. CRGreathouse (t | c) 03:26, 15 November 2007 (UTC)
How to denote shifted OEIS?[edit]
The number of the symmetric relations on an n element set is 2^(n-th triangular number), which is not in OEIS, only a shifted version of it. That is linked currently, but it is not denoted, that it is shifted. I am somehow satisfied how the template looks now, and I don't think it needs further clarification, yet, if there is a way for it, it can be done. Thanks, 157.181.151.144 (talk) 14:54, 9 November 2021 (UTC)
- The number of symmetric relations on an n-element set is A006125(n+1). - CRGreathouse (t | c) 16:17, 12 November 2021 (UTC)
number of irreflexive relations[edit]
It might be worth noting that the number of irreflexive relations is the same as the number of reflexive relations. Abm9856 (talk) 18:30, 3 December 2022 (UTC)