Question

some numbers can be expressed as the sum of a string of consecutive positive numbers which numbers have this property

Answer 1

K, so, lets add them up
1+2=3
1+2+3=6
1+2+3+4=10
1+2+3+4+5=15
1+2+3+4+5+6=21
1+2+3+4+5+6+7=28
etc

basically
all numbers 'x' such that
x=$\frac{(n+1)(n+2)}{2}$ and n is the set of all natural numbers