1-Even number

2-Prime number

3-Not prime

4-Non of these

Please explain yor answer

1-Even number

2-Prime number

3-Not prime

4-Non of these

Please explain yor answer

 

 

Not even and not prime. It is divisible by 1,111,111 amongst others

 

If R_n is the number 1....1 with n repetitions then it can be shown that if n is not prime (ie can be divided by a and b) then R_n is not prime and that R_n can be divided by R_a and R_b

It is obviously not even. And probably not prime.

 

In fact, not prime: http://www.wolframalpha.com/input/?i=is+1111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111+prime

It is obviously not even. And probably not prime.

 

In fact, not prime: http://www.wolframalpha.com/input/?i=is+1111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111+prime

 

I had forgotten about wolfram alpha - it can give me the actual result to my divisor 1,111,111

1000000100000010000001000000100000010000001000000100000010000001000000100000010000001 x 1111111

That is such a cool looking sum; and if you think about it - the pattern makes total sense

Please explain yor answer

 

Please explain your question!

thanks friends

1. It's not an even number because it ends with 1, it's an odd number

3. It's not a prime number because it's divisible by 1,111,111 other than 1

Primes of that form are are quite rare, see https://oeis.org/A004023 to find numbers of the form [math]111 \dots 111=\frac{10^n-1}{9}[/math] that are prime.
It turns out that this number is prime for n=2, 19, 23, 317, 1031, 49081, 86453, 109297 or 270343.

Edited October 8, 20169 yr by renerpho

Primes of that form are are quite rare, see https://oeis.org/A004023 to find numbers of the form [math]111 \dots 111=\frac{10^n-1}{9}[/math] that are prime.

It turns out that this number is prime for n=2, 19, 23, 317, 1031, 49081, 86453, 109297 or 270343.

 

Gotta love Sloane's. I hadn't realised they were so rare - just that it was relatively simple to show if the number had to be compound; obviously it is always simpler to show that a number is compound than to show that it is prime but in this case the test to show compound nature was so cute.