21157635437 has 4 divisors (see below), whose sum is σ = 21220418076. Its totient is φ = 21094852800.

The previous prime is 21157635427. The next prime is 21157635451. The reversal of 21157635437 is 73453675112.

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 2187807076 + 18969828361 = 46774^2 + 137731^2 .

It is a cyclic number.

It is not a de Polignac number, because 21157635437 - 2⁸ = 21157635181 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 (21157635407) 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, 31390814 + ... + 31391487.

It is an arithmetic number, because the mean of its divisors is an integer number (5305104519).

Almost surely, 2^21157635437 is an apocalyptic number.

It is an amenable number.

21157635437 is a deficient number, since it is larger than the sum of its proper divisors (62782639).

21157635437 is an equidigital number, since it uses as much as digits as its factorization.

21157635437 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 62782638.

The product of its digits is 529200, while the sum is 44.

The spelling of 21157635437 in words is "twenty-one billion, one hundred fifty-seven million, six hundred thirty-five thousand, four hundred thirty-seven".