21005431621 has 8 divisors (see below), whose sum is σ = 21036603200. Its totient is φ = 20974282560.

The previous prime is 21005431613. The next prime is 21005431631. The reversal of 21005431621 is 12613450012.

It is a happy number.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21005431621 - 2³ = 21005431613 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21005431631) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 2812390 + ... + 2819848.

It is an arithmetic number, because the mean of its divisors is an integer number (2629575400).

Almost surely, 2^21005431621 is an apocalyptic number.

It is an amenable number.

21005431621 is a deficient number, since it is larger than the sum of its proper divisors (31171579).

21005431621 is a wasteful number, since it uses less digits than its factorization.

21005431621 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 11259.

The product of its (nonzero) digits is 1440, while the sum is 25.

Adding to 21005431621 its reverse (12613450012), we get a palindrome (33618881633).

The spelling of 21005431621 in words is "twenty-one billion, five million, four hundred thirty-one thousand, six hundred twenty-one".