21078945 has 12 divisors (see below), whose sum is σ = 36536916. Its totient is φ = 11242080.

The previous prime is 21078931. The next prime is 21078947. The reversal of 21078945 is 54987012.

It can be written as a sum of positive squares in 2 ways, for example, as 4112784 + 16966161 = 2028^2 + 4119^2 .

It is not a de Polignac number, because 21078945 - 2⁹ = 21078433 is a prime.

It is a Smith number, since the sum of its digits (36) coincides with the sum of the digits of its prime factors.

It is an alternating number because its digits alternate between even and odd.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21078947) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 234166 + ... + 234255.

It is an arithmetic number, because the mean of its divisors is an integer number (3044743).

Almost surely, 2^21078945 is an apocalyptic number.

It is an amenable number.

21078945 is a deficient number, since it is larger than the sum of its proper divisors (15457971).

21078945 is a wasteful number, since it uses less digits than its factorization.

21078945 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 468432 (or 468429 counting only the distinct ones).

The product of its (nonzero) digits is 20160, while the sum is 36.

The square root of 21078945 is about 4591.1812205575. The cubic root of 21078945 is about 276.2377047960.

The spelling of 21078945 in words is "twenty-one million, seventy-eight thousand, nine hundred forty-five".