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

Composite numbers are opposite to prime numbers.

• ...,
• 1228,
• 1230,
• 1232,
• 1233,
• 1234,
• 1235,
• 1236,
• ...

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.

• ...,
• 1228,
• 1229,
• 1231,
• 1233,
• 1234,
• 1235,
• 1237,
• ...

One can take the sum of the squares of the digits of a number. Those numbers are happy for which iterating this operation eventually leads to 1.

• ...,
• 1218,
• 1221,
• 1222,
• 1233,
• 1247,
• 1251,
• 1257,
• ...

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.

• ...,
• 1209,
• 1219,
• 1231,
• 1233,
• 1245,
• 1249,
• 1251,
• ...

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.

• ...,
• 1227,
• 1229,
• 1231,
• 1233,
• 1235,
• 1237,
• 1239,
• ...

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

Guess what evil numbers are.

• ...,
• 1226,
• 1228,
• 1231,
• 1233,
• 1234,
• 1236,
• 1239,
• ...