Number Gossip

(Enter a number and I'll tell you everything you wanted to know about it but were afraid to ask.)

Unique Properties of 9009

9009 is the largest 4-digit palindrome which is also palindromic in binary (submitted by Andy Edwards)

Common Properties of 9009

Apocalyptic power

The number n is called an apocalyptic power if 2ⁿ contains the consecutive digits 666 (in decimal).

...,
9005,
9007,
9008,
9009,
9010,
9011,
9012,
...

Composite

A positive integer greater than 1 that is not prime is called composite.

Composite numbers are opposite to prime numbers.

...,
9005,
9006,
9008,
9009,
9010,
9012,
9014,
...

Deficient

The number n is deficient if the sum of all its positive divisors except itself is less than n.

Compare with perfect and abundant numbers.

...,
9005,
9007,
9008,
9009,
9010,
9011,
9013,
...

Evil

The number n is evil if it has an even number of 1's in its binary expansion.

Guess what odious numbers are.

...,
9002,
9004,
9007,
9009,
9010,
9012,
9015,
...

Lucky

To build the lucky number sequence, start with natural numbers. Delete every second number, leaving 1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, ... . The second number remaining is 3, so delete every third number, leaving 1, 3, 7, 9, 13, 15, 19, 21, ... . The next number remaining is 7, so delete every 7th number, leaving 1, 3, 7, 9, 13, 15, 21, ... . The next number remaining is 9, so delete every ninth number, etc.

Those numbers were lucky they weren't crossed out.

...,
8989,
8995,
8997,
9009,
9031,
9033,
9061,
...

Odd

A number is odd if it is not divisible by 2.

Numbers that are not odd are even. Compare with another pair -- evil and odious numbers.

...,
9003,
9005,
9007,
9009,
9011,
9013,
9015,
...

Palindrome

A palindrome is a number that reads the same forward or backward.

...,
8778,
8888,
8998,
9009,
9119,
9229,
9339,
...

Tanya Khovanova

Number Gossip

Unique Properties of 9009

Common Properties of 9009