Question 1195913
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Refer the "Many Rules" section of this page
<a href = "https://www.mathsisfun.com/algebra/sequences-finding-rule.html">https://www.mathsisfun.com/algebra/sequences-finding-rule.html</a>
and my response on this page
<a href = "https://www.algebra.com/algebra/homework/Sequences-and-series/Sequences-and-series.faq.question.1195799.html">https://www.algebra.com/algebra/homework/Sequences-and-series/Sequences-and-series.faq.question.1195799.html</a>
for explanations as to why there often isn't one set formula to follow when it comes to problems like this. Things are too vague and there are many possibilities here. 
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