Question 496961
Look it up on Google. The word "batty number" is either very rarely used or never used in mathematics.


Update: I looked it up; they are more often referred to as "vampire numbers." Not all the "numbers" are factors of the whole number, as you said (since 4 is not a factor of 1435), but rather, they satisfy this property:


1395 = 15*93
1435 = 35*41
2187 = 27*81


In each of these cases, the four-digit number is equal to the product of two two-digits numbers, such that the four digit number and the two-digit numbers use the same digits.