If $d(n)$ is the sum of digits of n, find $d(d(d(n)))$ of $n=4444^{4444}$
853
Write down the sum of sum of  sum of digits of $4444^{4444}$
103854
Showing that $Q_n=D_n+D_{n-1}$
108497
Can $2^n$ and $2^{n+1}$ have the same digit sum?
45240
Starting digits of $2^n$.
41571
Prove that in a sequence of numbers $49 , 4489 , 444889 , 44448889\ldots$
133937
Find the four digit number?
114277
Proving in Discrete Structures Problem that $2^N = \binom{N}{0} + \binom{N}{1} + \binom{N}{2} + \dots + \binom{N}{N}$
91285
Prove $a+b+c+d $ is composite
48605
Distinct digits in a combination of 6 digits
142151
Find the last two digits of $9^{{9}^{9}}$
4333
Prove that if $a+b+c+d=4$, then $(a^2+3)(b^2+3)(c^2+3)(d^2+3)\geq256$
14693
$d = \gcd(c,m),\ ac≡bc\pmod{\! m}\Rightarrow a≡b\pmod {\!m/d}\ $ [Congruence Cancellation & Division Rule]
19599
$ d(x_n,y_n) \to d(x,y)$ if $x_n\to x$ and $y_n \to y$
150289
A number with an interesting property. $abcd=a^b c^d$
93572
How to determine if $n (n \geq 2)$ given numbers can be summed up to a certain number?
7327
Sum of the digits of the number 2^1000
79568
Cardinality of the set $D$