21236400257 has 4 divisors (see below), whose sum is σ = 21259712256. Its totient is φ = 21213088260.

The previous prime is 21236400253. The next prime is 21236400287. The reversal of 21236400257 is 75200463212.

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 21236400257 - 2² = 21236400253 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21236400253) 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, 11654633 + ... + 11656454.

It is an arithmetic number, because the mean of its divisors is an integer number (5314928064).

Almost surely, 2^21236400257 is an apocalyptic number.

It is an amenable number.

21236400257 is a deficient number, since it is larger than the sum of its proper divisors (23311999).

21236400257 is an equidigital number, since it uses as much as digits as its factorization.

21236400257 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 23311998.

The product of its (nonzero) digits is 20160, while the sum is 32.

Adding to 21236400257 its reverse (75200463212), we get a palindrome (96436863469).

The spelling of 21236400257 in words is "twenty-one billion, two hundred thirty-six million, four hundred thousand, two hundred fifty-seven".