Question 1196058
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Another possible rule is to say that the given sequence lists 3 consecutive prime numbers in the descending order.


Then the expected next (and the last) term is 2.



Yet another possible formula is    {{{a[n]}}} = {{{5 + 2*sin((pi/2)*n)}}},   n = 1, 2, 3, 4, 5, . . . 

which gives the sequence repeating cyclically  7, 5, 3, 5, 7, 5, 3, 5 . . . 




Yet another formula is  {{{a[n]}}} = 7 - 2*(n-1) + (n-1)*(n-2)*(n-3)*F(n),

where F(n) is an arbitrary polynomial with integer coefficients.


It produces the same three values at n = 1,2,3, but gives totally different values at n > 3.




I write it to explain you that more than one million possible "rules" and "formulas" can be created.


And without a context or additional info, you do not know and can not know, which is right and what to select.



So, mathematically, the problem and the question are quite non-sensical.



For a mathematically educated person, it is very important to understand it clearly.