What is
special about the number 1395 ?
- Well 1395
= 15 x 93.
- It is
called a VAMPIRE number with fangs 15 and 93.
- Another
example is 1435 = 35 x 41 with the two fangs 35 and
41.
- If you
know the fangs, for example 30 and 51, its easy to
find the vampire...
- ...but if
you meet the vampire, for example 1827, can you find its
fangs?
- And how
easy is it to spot a vampire hiding among innocent numbers?
- For
instance which among 2155, 2170 and 2187 is the
vampire?
- Vampire numbers have an even number of digits
with their two fangs sharing half that number between
them.
- There are
exactly seven 4-digit vampire numbers. If you worked through the
examples above you should now know five of them. Can
you find the other two? One is less than 1395 and the
other ...?
- Some large
vampire numbers have a spare pair of
fangs...
- 125460 =
204 x 615 = 246 x 510
- or even
two spare pairs ...
- 13078260 =
1620 x 8073 = 1863 x 7020 = 2070 x 6318
- Now that
is amazing!
|
No
20
