21505550431 has 4 divisors (see below), whose sum is σ = 21506190552. Its totient is φ = 21504910312.

The previous prime is 21505550393. The next prime is 21505550453. The reversal of 21505550431 is 13405550512.

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 21505550431 - 2⁷ = 21505550303 is a prime.

It is a super-2 number, since 2×21505550431² (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 = 21505550393 and 21505550402.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21505550491) 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, 266701 + ... + 337846.

It is an arithmetic number, because the mean of its divisors is an integer number (5376547638).

Almost surely, 2^21505550431 is an apocalyptic number.

21505550431 is a deficient number, since it is larger than the sum of its proper divisors (640121).

21505550431 is an equidigital number, since it uses as much as digits as its factorization.

21505550431 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 640120.

The product of its (nonzero) digits is 15000, while the sum is 31.

The spelling of 21505550431 in words is "twenty-one billion, five hundred five million, five hundred fifty thousand, four hundred thirty-one".