21315021 has 32 divisors (see below), whose sum is σ = 35266560. Its totient is φ = 11150784.

The previous prime is 21315013. The next prime is 21315023. The reversal of 21315021 is 12051312.

It is not a de Polignac number, because 21315021 - 2³ = 21315013 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21315023) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 44260 + ... + 44738.

It is an arithmetic number, because the mean of its divisors is an integer number (1102080).

Almost surely, 2^21315021 is an apocalyptic number.

21315021 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

It is an amenable number.

21315021 is a deficient number, since it is larger than the sum of its proper divisors (13951539).

21315021 is a wasteful number, since it uses less digits than its factorization.

21315021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 665.

The product of its (nonzero) digits is 60, while the sum is 15.

The square root of 21315021 is about 4616.8193596891. The cubic root of 21315021 is about 277.2651303807.

Adding to 21315021 its reverse (12051312), we get a palindrome (33366333).

The spelling of 21315021 in words is "twenty-one million, three hundred fifteen thousand, twenty-one".