Added arithamatic Sequence C++

[H3MNT]

• [ ] Have you checked that there aren't other projects for the same topic in any language?
• [ ] Does your project contains a README and REQUIREMENTS file to help a newbie understand and execute your project code?
• [x] Have you tested your code locally within another machine for it to execute without changes/updates?
• [x] Does your code conform to the hacktoberfest rules?
• [ ] Do you accept that this code is not available elsewhere on internet and you completely owe the rights to this project code.

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