21237540221 has 4 divisors (see below), whose sum is σ = 21286588092. Its totient is φ = 21188492352.

The previous prime is 21237540211. The next prime is 21237540227. The reversal of 21237540221 is 12204573212.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 9194892100 + 12042648121 = 95890^2 + 109739^2 .

It is a cyclic number.

It is not a de Polignac number, because 21237540221 - 2¹⁴ = 21237523837 is a prime.

It is a super-2 number, since 2×21237540221² (a number of 21 digits) contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21237540227) 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, 24523286 + ... + 24524151.

It is an arithmetic number, because the mean of its divisors is an integer number (5321647023).

Almost surely, 2^21237540221 is an apocalyptic number.

It is an amenable number.

21237540221 is a deficient number, since it is larger than the sum of its proper divisors (49047871).

21237540221 is an equidigital number, since it uses as much as digits as its factorization.

21237540221 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 49047870.

The product of its (nonzero) digits is 6720, while the sum is 29.

The spelling of 21237540221 in words is "twenty-one billion, two hundred thirty-seven million, five hundred forty thousand, two hundred twenty-one".