Question 1156464
the difference between adjacent ones is 1/3/6/10/15/21. The next difference will be seven more from 21 or 28 and the term will ver 56+28, or 84.

The differences are
0
----1
1-------2
----3-------1

4-------3
----6-------1

10------4
----10------1
20-----5
----15-----1
35-----6
----21----1
56

This will be a cubic polynomial, because the third differences are equal: an^3+bn^2+cn+d=0
a=the third difference or 1
12a+2b is first second difference or 2
7a+3b+c=u2-u1 or 2-1 or 1
and a+b+c+d= u1, which is 0

6a=1 so a =(1/6)
12a+2b=2, and therefore 2b=0
7a+3b+c=1 and therefore (7/6)-c=1 and c=-(1/6)
a+b+c+d=0 and d will equal 0 as well.

The general formula is (1/6)n^3-(1/6)n
don't factor it out.  For n=1 to 6, the numbers will be the sequence

when n=8 it will be (1/6)512-(8/6). that is (512-8)/6=84.

Sorry I was on autopilot.  Hope that helps.