21004231521 has 128 divisors (see below), whose sum is σ = 36516888576. Its totient is φ = 10444723200.

The previous prime is 21004231499. The next prime is 21004231529. The reversal of 21004231521 is 12513240012.

It is not a de Polignac number, because 21004231521 - 2⁷ = 21004231393 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (21).

It is not an unprimeable number, because it can be changed into a prime (21004231529) by changing a digit.

It is a polite number, since it can be written in 127 ways as a sum of consecutive naturals, for example, 71686651 + ... + 71686943.

It is an arithmetic number, because the mean of its divisors is an integer number (285288192).

Almost surely, 2^21004231521 is an apocalyptic number.

21004231521 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

It is an amenable number.

21004231521 is a deficient number, since it is larger than the sum of its proper divisors (15512657055).

21004231521 is a wasteful number, since it uses less digits than its factorization.

21004231521 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 551.

The product of its (nonzero) digits is 480, while the sum is 21.

Adding to 21004231521 its reverse (12513240012), we get a palindrome (33517471533).

The spelling of 21004231521 in words is "twenty-one billion, four million, two hundred thirty-one thousand, five hundred twenty-one".