Material n = first material+(material number-1)* tolerance.

Number of items = (last item-first item)/tolerance+1

Tolerance = (last item-first item)/(number of items-1)

Arithmetic progression is a common series. If a series starts with the second item, the difference between each item and its previous item is equal to the same? Constant, this series is called arithmetic progression, and this constant is called arithmetic progression's tolerance, which is often represented by the letter D..

The general formula is: an = a1+(n-1) * D. The first term a 1= 1, and the tolerance d=2.

Derivation of general formula:

a2-a 1 = d； a3-a2 = d； A4-A3 = D...An-A (n- 1) = D, and the left and right sides of the above formula are respectively added to obtain an-a1= (n-1) * d → an = a1+(n-650

The first n terms and formulas are: sn = a1* n+[n * (n-1) * d]/2.

Sn=[n*(a 1+an)]/2

Sn=d/2*n？ +(a 1-d/2)*n

Note: All the above n are positive integers.