Chapter 9, Problem 13E

Consider the sequence $0,1,3,6,10,15,\mathrm{21...}$.

a. List the next two terms of the sequence.

b. Assuming that the sequence is denoted by $A_1,A_2,A_3,\mathrm{...}$, give an explicit formula for $A_N$.

c. Assuming that the sequence is denoted by $P_0,P_1,P_2,\mathrm{...}$, give an explicit formula for $P_N$.