21573759921 has 16 divisors (see below), whose sum is σ = 33638820864. Its totient is φ = 12041167824.

The previous prime is 21573759881. The next prime is 21573759959. The reversal of 21573759921 is 12995737512.

It is a happy number.

It is not a de Polignac number, because 21573759921 - 2⁹ = 21573759409 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21573759521) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 11944701 + ... + 11946506.

It is an arithmetic number, because the mean of its divisors is an integer number (2102426304).

Almost surely, 2^21573759921 is an apocalyptic number.

21573759921 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

It is an amenable number.

21573759921 is a deficient number, since it is larger than the sum of its proper divisors (12065060943).

21573759921 is a wasteful number, since it uses less digits than its factorization.

21573759921 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 23891260.

The product of its digits is 1190700, while the sum is 51.

The spelling of 21573759921 in words is "twenty-one billion, five hundred seventy-three million, seven hundred fifty-nine thousand, nine hundred twenty-one".