This question appeared in a competitive exam. The question is:
Q. Find the unknown term in $87,89,95,107,?,157$
$1$.) $127$ $\ \ \ \ \ \ \ \ $ $2.$) $122$
$3$.) $139$ $\ \ \ \ \ \ \ \ $ $4$.) $140$
I tried very much to solve it but can't find the correct answer. Any hints will be appreciated.
Thanks in advance.
Edit:
My effort that I did before asking this question:
I calculated the difference b/w consecutive terms. The diff is $2,6,12,20$. I was not able to recognize any pattern. After this I subtracted each term, which is less than $100$, from $100$ and, subtracted $100$ from each term which is greater than $100$. The resultant sequence is is $13,17,11,5,7,x,y$. Again I could not recognize any pattern.
Source
It was asked in SBI Clerical Exam on $\operatorname{May} 27, 2012$. It is the $110$th question of that exam.
The expected answer is probably something like this:
Each column is the difference of the previous column
However, we can fit any number in the unknown spot with the proper function. Each of the following polynomials has $f_k(0)=87$, $f_k(1)=89$, $f_k(2)=95$, $f_k(3)=107$, $f_k(5)=157$, yet $$\begin{array}{l} f_1(n)=87\binom{n}{0}+2\binom{n}{1}+4\binom{n}{2}+2\binom{n}{3}&\text{gives }f_1(4)=127\\ f_2(n)=87\binom{n}{0}+2\binom{n}{1}+4\binom{n}{2}+2\binom{n}{3}-5\binom{n}{4}+25\binom{n}{5}&\text{gives }f_2(4)=122\\ f_3(n)=87\binom{n}{0}+2\binom{n}{1}+4\binom{n}{2}+2\binom{n}{3}+12\binom{n}{4}-60\binom{n}{5}&\text{gives }f_3(4)=139\\ f_4(n)=87\binom{n}{0}+2\binom{n}{1}+4\binom{n}{2}+2\binom{n}{3}+13\binom{n}{4}-65\binom{n}{5}&\text{gives }f_4(4)=140\\ \end{array} $$ All the possible answers have an explanation in terms of these polynomials.