21020945 has 16 divisors (see below), whose sum is σ = 28408320. Its totient is φ = 14793600.

The previous prime is 21020941. The next prime is 21020947. The reversal of 21020945 is 54902012.

It is not a de Polignac number, because 21020945 - 2² = 21020941 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21020945.

It is not an unprimeable number, because it can be changed into a prime (21020941) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 4460 + ... + 7869.

It is an arithmetic number, because the mean of its divisors is an integer number (1775520).

Almost surely, 2^21020945 is an apocalyptic number.

It is an amenable number.

21020945 is a deficient number, since it is larger than the sum of its proper divisors (7387375).

21020945 is a wasteful number, since it uses less digits than its factorization.

21020945 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 12376.

The product of its (nonzero) digits is 720, while the sum is 23.

The square root of 21020945 is about 4584.8604122699. The cubic root of 21020945 is about 275.9841104414.

Adding to 21020945 its reverse (54902012), we get a palindrome (75922957).

The spelling of 21020945 in words is "twenty-one million, twenty thousand, nine hundred forty-five".