Those Fascinating Numbers 403
11 . . . 1
109 297
the eighth prime number whose digits are only 1’s (see the number 19).
2216 090(2216 091
1)
the
31rst
even perfect number, a 130 100 digit number.
2219
+ 1
the
20th
Fermat number, a 157 827 digit number; it is a composite number,
two of its prime factors are known, namely 70 525 124 609 = 33 629 ·
221
+ 1
(discovered by Riesel in 1962) and 646 730 219 521 = 308
385·221
+1 (discovered
by Wrathall in 1963); see the number 70 525 124 609.
2756 839
1
the
32nd
Mersenne prime, a 227 832 digit number.
2859 433 1
the
33rd
Mersenne prime, a 258 716 digit number.
11 . . . 1
270 343
the ninth prime number whose digits are only 1’s (see the number 19).
2220
+ 1
the
21rst
Fermat number, a 315 653 digit number; it is a composite number
(see the number 70 525 124 609).
21 257 787
1
the 34th Mersenne prime, a 378 632 digit number.
21 398 269
1
the
35th
Mersenne prime, a 420 921 digit number (see the number 1 398 269).
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