21015240021 has 32 divisors (see below), whose sum is σ = 32239171200. Its totient is φ = 13513651200.

The previous prime is 21015239969. The next prime is 21015240041. The reversal of 21015240021 is 12004251012.

21015240021 is a `hidden beast` number, since 210 + 1 + 52 + 400 + 2 + 1 = 666.

It is not a de Polignac number, because 21015240021 - 2¹⁴ = 21015223637 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21015239976 and 21015240003.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21015240041) 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, 810165 + ... + 835701.

It is an arithmetic number, because the mean of its divisors is an integer number (1007474100).

Almost surely, 2^21015240021 is an apocalyptic number.

It is an amenable number.

21015240021 is a deficient number, since it is larger than the sum of its proper divisors (11223931179).

21015240021 is a wasteful number, since it uses less digits than its factorization.

21015240021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 26626 (or 26620 counting only the distinct ones).

The product of its (nonzero) digits is 160, while the sum is 18.

Adding to 21015240021 its reverse (12004251012), we get a palindrome (33019491033).

The spelling of 21015240021 in words is "twenty-one billion, fifteen million, two hundred forty thousand, twenty-one".