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.

• ...,
• 3567,
• 3568,
• 3569,
• 3571,
• 3572,
• 3573,
• 3574,
• ...

The n-th lazy caterer number is the maximum number of pieces a (circular) pizza can be cut into with n (straight-line) cuts.

Unlike the situation with cake, everybody gets the toppings.

• ...,
• 3322,
• 3404,
• 3487,
• 3571,
• 3656,
• 3742,
• 3829,
• ...

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.

• ...,
• 3507,
• 3559,
• 3565,
• 3571,
• 3579,
• 3595,
• 3597,
• ...

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.

• ...,
• 3565,
• 3567,
• 3569,
• 3571,
• 3573,
• 3575,
• 3577,
• ...

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

Guess what evil numbers are.

• ...,
• 3565,
• 3566,
• 3568,
• 3571,
• 3573,
• 3574,
• 3577,
• ...

A prime is a positive integer greater than 1 that is divisible by no positive integers other than 1 and itself.

Prime numbers are opposite to composite numbers.

• ...,
• 3547,
• 3557,
• 3559,
• 3571,
• 3581,
• 3583,
• 3593,
• ...

A number is said to be square-free if its prime decomposition contains no repeated factors.

• ...,
• 3567,
• 3569,
• 3570,
• 3571,
• 3574,
• 3578,
• 3579,
• ...