Aptitude - Numbers - Discussion

@Raji thanks.

Thank you dilipkumar

Can we use this shortcut for 3 and 4 digits?

@Dilipkumar(Cse).

That is an awesome way to remember all prime numbers between 1 & 100. There is a pattern too.

Table of Prime Number up to 1000.

2 3 5 7 11 13 17 19 23
29 31 37 41 43 47 53 59 61 67
71 73 79 83 89 97 101 103 107 109
113 127 131 137 139 149 151 157 163 167
173 179 181 191 193 197 199 211 223 227
229 233 239 241 251 257 263 269 271 277
281 283 293 307 311 313 317 331 337 347
349 353 359 367 373 379 383 389 397 401
409 419 421 431 433 439 443 449 457 461
463 467 479 487 491 499 503 509 521 523
541 547 557 563 569 571 577 587 593 599
601 607 613 617 619 631 641 643 647 653
659 661 673 677 683 691 701 709 719 727
733 739 743 751 757 761 769 773 787 797
809 811 821 823 827 829 839 853 857 859
863 877 881 883 887 907 911 919 929 937
941 947 953 967 971 977 983 991 997

@Santhosh @Raji thanks for help.

But it only possible for some hundreds.

When we find 9999 is prime no or not,

It takes lot of time.

n*n>= p.
n*n>= 9999.
Where n must be 100.

So there are many prime no below 100.
To divided by no.

So it is not possible for all no.

Please post another method if you knew.

It is not possible for all numbers.

Please give me detailed explanation about prime number.

If any given number is prime or not, how can u find out? here is one way to solve for that one.

Step 1:

Find the square root for given number. if it is not a perfect square take nearest number of that on.

Ex: 91 is given. 8 is nearest square root (81) [91<x^2]

Step 2:

Write all prime numbers below that square root number.

2 3 5 7

Step 3:

If the given number(91) is not divisible with any one of the above numbers(2 3 5 7) then that number is prime number otherwise it's not.

Simple meaning of prime no-"The number which is only divisible by itself and by 1, is called a prime number".