65. What whole number is equal to the sum of all the whole numbers preceding it? Is there only one such number?
65. $1+2=3$. No other number $>3$ has the required property: indeed, if we move forward in the sequence of natural numbers, then with each step taken, the sum of natural numbers increases by $3, 4, 5$, etc., while each subsequent natural number increases only by 1, and therefore the difference between the sum of natural numbers preceding a given number and this number will continue to grow. -Otherwise: the sum of integers preceding the number $n$ is $\frac{(n-1) n}{2}$. If it is to equal $n$, then $\frac{n-1}{2}=1$, from which $n-1=2, \quad n=3$