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

Composite numbers are opposite to prime numbers.

• ...,
• 778,
• 779,
• 780,
• 781,
• 782,
• 783,
• 784,
• ...

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.

• ...,
• 777,
• 778,
• 779,
• 781,
• 782,
• 783,
• 785,
• ...

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.

• ...,
• 667,
• 704,
• 742,
• 781,
• 821,
• 862,
• 904,
• ...

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.

• ...,
• 745,
• 769,
• 777,
• 781,
• 787,
• 801,
• 805,
• ...

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.

• ...,
• 775,
• 777,
• 779,
• 781,
• 783,
• 785,
• 787,
• ...

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

Guess what evil numbers are.

• ...,
• 775,
• 776,
• 779,
• 781,
• 782,
• 784,
• 787,
• ...

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

• ...,
• 777,
• 778,
• 779,
• 781,
• 782,
• 785,
• 786,
• ...

The next Ulam number is uniquely the sum of two earlier distinct Ulam numbers.

• ...,
• 734,
• 739,
• 751,
• 781,
• 783,
• 798,
• 800,
• ...