Dn denotes the squares of a 2-by-n board using plain dominos. Then we see D1 = 1, D2= 2, and D3 = 3. find more values of Dn and guess an expression.
71221
Find a recurrence relation for the number of ways to arrange $n$ dominoes to fill a $2$ by $n$ checkerboard.
97667
If $a<b$, $c<d$ then $a+c<b+d$?
85076
Is it true that $d(x,Y)=d(x,y_0)$ for some $y_0 \in Y$ when $Y$ is closed?
138256
What's the difference between $\mathbb{Q}[\sqrt{-d}]$ and $\mathbb{Q}(\sqrt{-d})$?
135212
The square of an integer has form $3n$ or $3n+1$
82327
Tiling a $3 \times 2n$ rectangle with dominoes
57236
How many different combinations of a six sided die rolls equals n
106416
If $n,m \in \mathbb{N}$ then there are $c,d$ such that $cd = (m,n)$, $(c,d) = 1$ and $(m/c,n/d) = 1$.
51816
Meaning of probability notations $P(z;d,w)$ and $P(z|d,w)$
79568
Cardinality of the set $D$
71534
Combinatorial explanation for why $n^2 = {n \choose 2} + {n+1 \choose 2}$
97805
$n+1$ is a divisor of $\binom{2n} {n}$
19599
$ d(x_n,y_n) \to d(x,y)$ if $x_n\to x$ and $y_n \to y$
112631
Prove that if $d$ divides $n$, then $2^d -1$ divides $2^n -1$
101394
Please explain the logic behind $d(xy) = y(dx) + x(dy)$
59479
For a positive integer $n\geq 2$ with divisors $1=d_1<d_2<\cdots<d_k=n$, prove that $d_1d_2+d_2d_3+\cdots+d_{k-1}d_k<n^2$
84092
If $id:(X,d_1)\to (X,d_2)$ is continuous then what will be $X$?