Those Fascinating Numbers 399
2213
+ 1
the
14th
Fermat number, a 2 467 digit number; it is a composite number, whose
smallest prime factor, namely
2 710 954 639 361 = 41 365 885 ·
216
+ 1,
was obtained by Hallyburton and Brillhart in 1963
(see the number 70 525 124 609).
24 252(24 253
1)
the 19th even perfect number, a 2 561 digit number.
24 422(24 423 1)
the
20th
even perfect number, a 2 663 digit number.
29 689
1
the 21rst Mersenne prime, a 2 917 digit number.
29 941 1
the 22nd Mersenne prime, a 2 993 digit number.
211 213
1
the 23rd Mersenne prime, a 3 376 digit number.
2214
+ 1
the
15th
Fermat number, a 4 933 digit number; it is a composite number (Self-
ridge and Hurwitz, 1963), of which no prime factor is known as of today.
29 688(29 689 1)
the 21rst even perfect number, a 5 834 digit number.
29 940(29 941 1)
the
22nd
even perfect number, a 5 985 digit number.
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