154 Jean-Marie De Koninck
3 217
the exponent of the
18th
Mersenne prime
23 217
1 (Riesel, 1957).
3 229
the 11th prime number pk such that p1p2 . . . pk + 1 is prime (see the number
379).
3 237
the second solution of σ2(n) = σ2(n + 6) (see the number 645).
3 250
the
12th
number n such that f(n) f(m) for all numbers m n, where
f(n) :=
Σ∗
1
p
, where the star indicates that the sum runs through all the prime
numbers p n which do not divide
(
2n
n
)
: here f(3250) = 1.17924 . . . (see the
number 364).
3 255
the
14th
solution of φ(n) = φ(n + 1) (see the number 15).
3 315
the smallest solution of σ(n + 49) = σ(n) + 49.
3 363
the eighth number n such that
n2
1 is powerful (see the number 485): here
3
3632
1 =
23
·
292
·
412.
3 371
the fifth prime number q such that

p≤q
p is a multiple of 100 (see the number
563).
3 375
the fourth odd number n 1 such that γ(n)|σ(n) (see the number 135).
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