Question 16
For natural $n$, consider
$A=37^n+71^n-2^n-1$;
$B=n(n^2-6)^2(n^2-1)-n^3(n-1)(n+1)$;
$C=1+2+\cdots+(21n+1)$.
Which expressions are always divisible by $21$?
$A=37^n+71^n-2^n-1$;
$B=n(n^2-6)^2(n^2-1)-n^3(n-1)(n+1)$;
$C=1+2+\cdots+(21n+1)$.
Which expressions are always divisible by $21$?