162 Jean-Marie De Koninck
4 481
the sixth prime number of the form
(x4
+
y4)/2:
here 4 481 =
(74
+
94)/2
(see
the number 41).
4 503
the third number n such that n, n + 1, n + 2 and n + 3 have the same number
of divisors, in this case eight (see the number 242).
4 547
the
12th
prime number pk such that p1p2 . . . pk + 1 is prime (see the number
379).
4 550
the smallest number n which allows the sum
i≤n
1
i
to exceed 9 (see the number
83).
4 567
the only four digit prime number, whose digits are consecutive (see the number
67).
4 583
the
15th
prime number pk such that p1p2 . . . pk 1 is prime (see the number
317).
4 649
the largest prime factor of 1234567654321.
4 650
the smallest number n such that

m≤n
τ (m) is a multiple of 10 000 (here the
sum is equal to 40 000).
4 680 (=
23
·
32
· 5 · 13)
the second solution of
σ(n)
n
=
7
2
(see the number 4 320).
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