21012055531 has 4 divisors (see below), whose sum is σ = 21736609200. Its totient is φ = 20287501864.

The previous prime is 21012055511. The next prime is 21012055553. The reversal of 21012055531 is 13555021012.

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

It is a cyclic number.

It is not a de Polignac number, because 21012055531 - 2²⁵ = 20978501099 is a prime.

It is a super-2 number, since 2×21012055531² (a number of 21 digits) contains 22 as substring.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21012055496 and 21012055505.

It is not an unprimeable number, because it can be changed into a prime (21012055501) 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, 362276791 + ... + 362276848.

It is an arithmetic number, because the mean of its divisors is an integer number (5434152300).

Almost surely, 2^21012055531 is an apocalyptic number.

21012055531 is a deficient number, since it is larger than the sum of its proper divisors (724553669).

21012055531 is an equidigital number, since it uses as much as digits as its factorization.

21012055531 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 724553668.

The product of its (nonzero) digits is 1500, while the sum is 25.

Adding to 21012055531 its reverse (13555021012), we get a palindrome (34567076543).

The spelling of 21012055531 in words is "twenty-one billion, twelve million, fifty-five thousand, five hundred thirty-one".