21436420021 has 4 divisors (see below), whose sum is σ = 21892514112. Its totient is φ = 20980325932.

The previous prime is 21436420007. The next prime is 21436420063. The reversal of 21436420021 is 12002463412.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21436420021 - 2²⁷ = 21302202293 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 (21436420001) 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, 228046975 + ... + 228047068.

It is an arithmetic number, because the mean of its divisors is an integer number (5473128528).

Almost surely, 2^21436420021 is an apocalyptic number.

It is an amenable number.

21436420021 is a deficient number, since it is larger than the sum of its proper divisors (456094091).

21436420021 is an equidigital number, since it uses as much as digits as its factorization.

21436420021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 456094090.

The product of its (nonzero) digits is 2304, while the sum is 25.

Adding to 21436420021 its reverse (12002463412), we get a palindrome (33438883433).

The spelling of 21436420021 in words is "twenty-one billion, four hundred thirty-six million, four hundred twenty thousand, twenty-one".