228 Jean-Marie De Koninck
78 975
the fifth of the existing eight primitive non deficient numbers (see the number
945).
78 989
the largest five digit prime number whose digits are consecutive (see the number
67).
79 196
the second number n 1 such that
n2
+3 is a powerful number: here 79
1962
+
3 =
73
·
192
·
373
(see the number 37).
79 427
the fourth prime number q such that

p≤q
p is a perfect square: here

p≤79427
p = 292341604 = 170982 (see the number 22 073).
79 800
the smallest number n such that the Liouville function λ0 takes successively,
starting with n, the values 1, −1, 1, −1, 1, −1, 1, −1, 1, −1, 1, −1, 1, −1 (see the
number 6 185).
80 518
the only number of the form abcde such that abcde = a! b! c! d! + e!; here
80 518 = 8! 0! 5! 1! + 8! (see the number 40 585).
80 782
the seventh solution y of the Fermat-Pell equation x2 2y2 = 1, namely that
given by (x, y) = (114243, 80782) (see the number 99).
81 081 (= 34 · 7 · 11 · 13)
the smallest odd abundant number which is not divisible by 5: the sequence
of numbers satisfying this property begins as follows: 81 081, 153 153, 171 171,
189 189, 207 207, 223 839, 243 243, 261 261, 279 279, 297 297, 351 351 459 459,
513 513, 567 567, 621 621, 671 517, 729 729, 742 203, 783 783, 793 611, 812 889,
837 837, 891 891, 908 523, 960 687, 999 999, . . . (see the numbers 945 and
5 391 411 025).
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