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 1369

1369 is the only 4-digit square whose digits are increasing

Rare Properties of 1369

Square

The number n is a square if it is the square of an integer.

...,
1156,
1225,
1296,
1369,
1444,
1521,
1600,
...

Common Properties of 1369

Composite

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

Composite numbers are opposite to prime numbers.

...,
1365,
1366,
1368,
1369,
1370,
1371,
1372,
...

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.

...,
1365,
1366,
1367,
1369,
1370,
1371,
1373,
...

Evil

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

Guess what odious numbers are.

...,
1363,
1365,
1366,
1369,
1370,
1372,
1375,
...

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.

...,
1339,
1357,
1365,
1369,
1387,
1389,
1395,
...

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.

...,
1363,
1365,
1367,
1369,
1371,
1373,
1375,
...

Powerful

An integer n is powerful if for every prime p dividing n, p² also divides n.

How much power? They all can be written as a² b³.

...,
1323,
1331,
1352,
1369,
1372,
1444,
1521,
...

Tanya Khovanova

Number Gossip

Unique Properties of 1369

Rare Properties of 1369

Common Properties of 1369