Those Fascinating Numbers 279
1 456 728
the smallest 6-composite number n such that n + 2 is also 6-composite: here
1 456 728 = 23 · 3 · 7 · 13 · 23 · 29 and 1 456 730 = 2 · 5 · 11 · 17 · 19 · 41 (see the
number 1 428).
1 570 153 (= 13 · 269 · 449)
the smallest hyperperfect number having exactly three distinct prime factors
(it is the third 12-hyperperfect number).
1 571 328 (= 29 · 32 · 11 · 31)
the third solution of
σ(n)
n
=
13
4
(see the number 360);
the eighth Erd˝ os-Nicolas number (see the number 2 016).
1 590 816
the ninth number n such that φ(n) + σ(n) = 3n (see the number 312).
1 630 622
the eighth composite number n such that σ(n + 6) = σ(n) + 6 (see the number
104).
1 644 919
the 1 000
000th
square-free number (see the number 165).
1 671 800
the smallest multiple of 100 which is followed by at least 100 composite numbers
(see the number 370 261).
1 679 616
(=364)
the largest number n whose sum of digits is equal to
4

n (see the number 2 401).
1 741 725
the smallest number n 1 which can be written as the sum of the seventh
powers of its digits: the others are 4 210 818, 9 800 817, 9 926 315 and 14 459 929.
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