142 Jean-Marie De Koninck
2 057
the number of pseudoprimes in base 2 smaller than 108 (see the number 245).
2 080
the smallest number n 1 such that
γ(n)2|σ2(n);
the sequence of numbers
satisfying this property begins as follows: 1, 2 080, 2 100, 6 912, 16 800, 18 900,
21 600, 34 300, 52 000, 64 000, . . .
2 083
the prime number which appears the most often as the
13th
prime factor of an
integer (see the number 199).
2 089
the largest prime factor of the Mersenne number 229 1, whose complete fac-
torization is given by
229
1 = 233 · 1103 · 2089.
2 099
the fourth prime number q such that

p≤q
p is a multiple of 100: here this sum
is equal to 305 800 (see the number 563).
2 102 (= 2 · 1051)
the 1
000th
number having exactly two distinct prime factors (see the number
184).
2 127
the sixth number n such that 2n + n2 is prime (see the number 2 007).
2 131
the second odd number k such that 2n + k is composite for all numbers n k
(see the number 773); in fact the smallest number n such that 2n + 2131 is
prime (if any exists !) is larger than 4 400.
2 133 (= 33 · 79)
the second 2-hyperperfect number (see the number 21).
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