284 Jean-Marie De Koninck
2 744 210
the ninth solution y of the Fermat-Pell equation
x2

2y2
= 1: here (x, y) =
(3880899, 2744210); see the number 99.
2 759 640
one of the three numbers n such that the polynomial x5 −x±n can be factored:
the other two are n = 15 and n = 22 440: here x5 x ± 2 759 640 = (x2 ± 12x +
377)(x3 12x2 233x ± 7320) (see the number 22 440).
2 806 861
the fourth prime number p such that 31p−1 1 (mod p2) (see the number
79).
2 836 295
the third number which can be written as the sum of the cubes of its prime
factors: 2 836 295 = 5 · 7 · 11 · 53 · 139 =
53
+
73
+
113
+
533
+
1393
(see the
number 378).
2 879 865
the smallest Niven number n such that n + 90 is also a Niven number, while
no others are located in between (see the number 28 680).
2 890 625
the smallest seven digit automorphic number: 2 890 6252 = 8 355 712 890 625
(see the number 76).
2 914 393
the second and largest prime number p
232
such that
97p−1
1 (mod
p2)
(see Ribenboim [169], p. 347): the smallest is p = 7.
2 976 221
the exponent of the
36th
Mersenne prime
22 976 221
1 discovered by Spencer
in 1997 using the programme developed by G.F. Woltman (see the number
1 398 269).
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