21002051431 has 4 divisors (see below), whose sum is σ = 21053401600. Its totient is φ = 20950701264.

The previous prime is 21002051423. The next prime is 21002051449. The reversal of 21002051431 is 13415020012.

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 21002051431 - 2³ = 21002051423 is a prime.

It is a super-2 number, since 2×21002051431² (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 = 21002051399 and 21002051408.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21002054431) 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, 25674471 + ... + 25675288.

It is an arithmetic number, because the mean of its divisors is an integer number (5263350400).

Almost surely, 2^21002051431 is an apocalyptic number.

21002051431 is a deficient number, since it is larger than the sum of its proper divisors (51350169).

21002051431 is an equidigital number, since it uses as much as digits as its factorization.

21002051431 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 51350168.

The product of its (nonzero) digits is 240, while the sum is 19.

Adding to 21002051431 its reverse (13415020012), we get a palindrome (34417071443).

The spelling of 21002051431 in words is "twenty-one billion, two million, fifty-one thousand, four hundred thirty-one".