238 Jean-Marie De Koninck
114 689
the smallest prime factor of F12 =
2212
+ 1, which in particular is the smallest
Fermat number for which the complete factorization is not yet known (see the
number 70 525 124 609).
115 921 (= 13 · 37 · 241)
the fourth pseudoprime in bases 2, 3, 5 and 7 (see the number 29 341).
115 975
the tenth Bell number (see the number 52).
119 972
the smallest Niven number n such that n +40 is also a Niven number, but with
no others in between (see the number 28 680).
120 120 (=
23
· 3 · 5 · 7 · 11 · 13)
the smallest number n such that Ω(n)ω(n) 2n: here Ω(n)ω(n)/n 2.18235;
the sequence of numbers satisfying this inequality begins as follows: 120 120,
240 240, 480 480, 1 021 020, 2 042 040, . . . (to discover the smallest number n
such that
Ω(n)ω(n)
n, see the number 60; as for the maximal value of the
quantity
Ω(n)ω(n)/n,
see the number 3 569 485 920);
the smallest number n such that σ(n) = 21 · φ(n) (see the number 416 640).
121 056
the fifth number n such that φ(n)σ(n) is a fourth power: φ(121 056)σ(121 056) =
3364 (see the number 170).
123 653
the largest known prime number p such that
12p−1
1 (mod
p2):
the only
other prime number p
232
satisfying this property is 2 693 (see Ribenboim
[169], p. 347).
128 205
the second number which quadruples when its last digit is moved in first position
(see the number 102 564).
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