Prime Numbers

A prime number can be divided, without a remainder, only by itself and by 1. For example, 17 can be divided only by 17 and by 1.

>The only even prime number is 2. All other even numbers can be divided by 2.
  • If the sum of a number's digits is a multiple of 3, that number can be divided by 3.
  • No prime number greater than 5 ends in a 5. Any number greater than 5 that ends in a 5 can be divided by 5.
  • Zero and 1 are not considered prime numbers.
  • Except for 0 and 1, a number is either a prime number or a composite number. A composite number is defined as any number, greater than 1, that is not prime.

    • To prove whether a number is a prime number, first try dividing it by 2, and see if you get a whole number. If you do, it can't be a prime number. If you don't get a whole number, next try dividing it by prime numbers: 3, 5, 7, 11 (9 is divisible by 3) and so on, always dividing by a prime number (see table below).

    Here is a table of all prime numbers up to 1,000:

     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  

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    Decimal PlacesNumbersWorld's Largest Known Prime Number