21502153721 has 4 divisors (see below), whose sum is σ = 21502547712. Its totient is φ = 21501759732.

The previous prime is 21502153669. The next prime is 21502153747. The reversal of 21502153721 is 12735120512.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21502153721 - 2¹⁸ = 21501891577 is a prime.

It is a super-2 number, since 2×21502153721² (a number of 21 digits) contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21502153781) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 98825 + ... + 229718.

It is an arithmetic number, because the mean of its divisors is an integer number (5375636928).

Almost surely, 2^21502153721 is an apocalyptic number.

It is an amenable number.

21502153721 is a deficient number, since it is larger than the sum of its proper divisors (393991).

21502153721 is an equidigital number, since it uses as much as digits as its factorization.

21502153721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 393990.

The product of its (nonzero) digits is 4200, while the sum is 29.

The spelling of 21502153721 in words is "twenty-one billion, five hundred two million, one hundred fifty-three thousand, seven hundred twenty-one".