Question

:Help...........for how many positive integers n is n^3 -8n^2+20n-13 a prime number??

Answer 1

factorize it

Answer 2

how watever i get is not a prime number

Answer 3

why?

Answer 4

oh

Answer 5

but then ii have to plug in millions of values

Answer 6

what u want to calculate

Answer 7

(n^3 -8n^2+20n-13) a prime number

Answer 8

or n is a prime number

Answer 9

for n i will have to put millions of values to find how may n positive integers satisfy n^3 -8n^2+20n-13 to be a prime number

Answer 10

ok

Answer 11

so,what to do??

Answer 12

anything i can do to narrow down the possobilities

Answer 13

no answer given....

Answer 14

ok see for 2 it is prime number

Answer 15

wait i took wrong concept

Answer 16

\[(x-1) \times [(x-7)x + 13]\]

Answer 17

where x is n

Answer 18

ok

Answer 19

now see the first term is (x-1).
and other than 2 no other even number is a prime number right

Answer 20

i got the answer

Answer 21

no n does not have to be a prime number n^3 -8n^2+20n-13 has to be a prime number

Answer 22

yeah i know
(x−1)×[(x−7)x+13]
it has to be prime

Answer 23

yup so x can be anything greater or equal to 2

Answer 24

first term is (x-1) and two is the only even prime number.

Answer 25

but if u will subtract 1 from any other prime number the resultant will be divisible by 2

Answer 26

getting my point or not

Answer 27

x can be 4

Answer 28

yeah u r right

Answer 29

it means that for any odd integer other than 3 u will not get a prime number

Answer 30

yeah

Answer 31

Superb sheggy!

Answer 32

also the number cannot be graeter than 7

Answer 33

oh yeah

Answer 34

thanks fool bhai

Answer 35

so u are having a limited space to work out that is from 1 to 7

Answer 36

yes sheg u got it so answer is n=2,3,4

Answer 37

no actually 2 to 7

Answer 38

hahahaa right 2 to 7

Answer 39

but for 7 it will be 0

Answer 40

wait why cant it be greater than 7?

Answer 41

try any number u will get the answer

Answer 42

odd numbers cannot be included ok thats true

Answer 43

as i had told u any odd number subtracted by one will result in even number so it will be divisible by 2.........do u accept it or not

Answer 44

is 323 a prime number?

Answer 45

yeah i acept

Answer 46

its not div by 17

Answer 47

323 is divisible by 17

Answer 48

so 323 is not a prime number

Answer 49

4387
?

Answer 50

what u have put x = ??

Answer 51

n=20

Answer 52

1443?

Answer 53

gtg shall come bak in 15 min

Answer 54

for n = 20 it should be equal to 5187

Answer 55

oh yeah 1443?

Answer 56

no

Answer 57

20^3 - 8*20^2 + 20*20 -13
=8000 - 3200 + 400 -13
= 8400 - 3213
= 5187

Answer 58

gtg cum bak in 15 mins

Answer 59

dear i had told u for no value greater than 7 it would fit

Answer 60

and both 1443 and 5187 is divisible by 3

Answer 61

i am bak
so what to do now?

Answer 62

for no value greater than 7 that too even number it will not be a prime number

Answer 63

http://www.wolframalpha.com/input/?i=x^3-8x^2%2B20x-13+where+x+%3D+20
visit this website and plug in different value of x u will get the answer

Answer 64

king u there