280 Jean-Marie De Koninck
1 747 591
the third prime number p such that
13p−1
1 (mod
p2)
(see the number
863).
1 782 144 (= 27 · 32 · 7 · 13 · 17)
the second solution of
σ(n)
n
=
15
4
(see the number 293 760).
1 799 938 (= 2 · 7 · 83 · 1549)
the number n which allows the sum
m≤n
Ω(m)=4
1
m
to exceed 2 (see the number
10 305).
1 825 200
the ninth powerful number n such that n + 1 is also powerful: here 1 825 200 =
24 · 33 · 52 · 132 and 1 825 201 = 72 · 1932 (see the number 288).
1 835 421
the smallest number n which allows the sum
i≤n
1
i
to exceed 15 (see the num-
ber 83).
1 854 699
the third number n for which ξ(n) is an integer (see the number 614 341).
1 940 450
the ninth number n such that the binomial coefficient
(
n
2
)
is a perfect square:
here
(1
940 450
2
)
=
13721052
(see the number 289).
1 950 625 (= 54 · 3121)
the smallest 4-hyperperfect number: we say that a number n is 4-hyperperfect
if it can be written as n = 1 + 4
d|n
1dn
d (which is equivalent to the condition
4σ(n) = 5n + 3).
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