how to calculate nth term of this series?

general
1

0,1,2,4,6,9,12,16,20,25,30,36,42,49,56,64,72,81,90?

How to calculate nth term of this series can anyone help with explanation?

2

If you carefully observe the difference between adjacent elements forms a series and that looks like

0,1,1,2,2,3,3,4,4,5,5,6,6,7,7,…

nth in the initial series is equal to the sum of first n terms in the above series and that can be done easily. If you still have any doubt please do comment and here is the link to my solution.

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3

if n is even then nth term=(n/2)^2

if n is odd then nth term=(n-1)/2 * (n+1)/2

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