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Dear visitor,
looking into your post, it seems to me that you at the first time in your life see a math formula and try to write it,
using the keyboard of your computer.
What are you doing at this forum ?
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For your info :
(a) a^n means , and is used ONLY for this purpose: to show raising in degree "n".
For example, 2^2 = = 4; 3^2 = = 9.
(b) If you want to show the n-th term of a progression / (of a sequence), write a[n] or a(n).
We, the tutors, will read it as .