21549359209 has 27 divisors (see below), whose sum is σ = 25528910967. Its totient is φ = 18137062944.

The previous prime is 21549359197. The next prime is 21549359269. The reversal of 21549359209 is 90295394512.

The square root of 21549359209 is 146797.

It is a perfect power (a square), and thus also a powerful number.

It can be written as a sum of positive squares in only one way, i.e., 137475625 + 21411883584 = 11725^2 + 146328^2 .

It is not a de Polignac number, because 21549359209 - 2⁷ = 21549359081 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (49).

It is not an unprimeable number, because it can be changed into a prime (21549359269) by changing a digit.

It is a polite number, since it can be written in 26 ways as a sum of consecutive naturals, for example, 68847637 + ... + 68847949.

It is an arithmetic number, because the mean of its divisors is an integer number (945515221).

Almost surely, 2^21549359209 is an apocalyptic number.

21549359209 is the 146797-th square number.

21549359209 is the 73399-th centered octagonal number.

It is an amenable number.

21549359209 is a deficient number, since it is larger than the sum of its proper divisors (3979551758).

21549359209 is an frugal number, since it uses more digits than its factorization.

21549359209 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 774 (or 387 counting only the distinct ones).

The product of its (nonzero) digits is 874800, while the sum is 49.

Multiplying 21549359209 by its sum of digits (49), we get a square (1055918601241 = 1027579²).

21549359209 divided by its sum of digits (49) gives a square (439782841 = 20971²).

The spelling of 21549359209 in words is "twenty-one billion, five hundred forty-nine million, three hundred fifty-nine thousand, two hundred nine".