174 Jean-Marie De Koninck
6 880
the largest four digit vampire number: here 6 880 = 86 · 80 (see the number
1 260).
6 912
the seventh number n 1 such that φ(σ(n)) = n (see the number 128).
6 917
the
21rst
number n such that n! 1 is prime (see the number 166).
6 930
the fifth solution w of the aligned houses problem (see the number 35).
6 977
the seventh prime number q such that

p≤q
p is a multiple of 100 (see the
number 563).
7 022
the largest number n for which inequality pn n(log n+log log n−0.9385) does
not hold: here p7022 = 70919 7022(log 7022+log log 7022−0.9385) = 70918.6
(see G. Robin [175]).
7 055
the seventh Lucas-Carmichael number (see the number 399).
7 140
one of the five numbers (the others are 1, 10, 120 and 1 540) which are both
triangular and tetrahedral (see the number 10).
7 192
the fifth bizarre number (see the number 70).
7 225
the smallest perfect square m4
2
for which there exist numbers m1, m2, m3 such
that mi
2
(mi
1)2
= mi−1
2
for i = 2, 3, 4: here 7 225 =
852
=
842
+
132
=
842 + 122 + 52 = 842 + 122 + 42 + 32 (see the number 169).
Previous Page Next Page