21400243 has 4 divisors (see below), whose sum is σ = 21413248. Its totient is φ = 21387240.

The previous prime is 21400219. The next prime is 21400271. The reversal of 21400243 is 34200412.

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 21400243 - 2¹³ = 21392051 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21400343) 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, 3603 + ... + 7468.

It is an arithmetic number, because the mean of its divisors is an integer number (5353312).

Almost surely, 2^21400243 is an apocalyptic number.

21400243 is a deficient number, since it is larger than the sum of its proper divisors (13005).

21400243 is a wasteful number, since it uses less digits than its factorization.

21400243 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 13004.

The product of its (nonzero) digits is 192, while the sum is 16.

The square root of 21400243 is about 4626.0396669289. The cubic root of 21400243 is about 277.6341607049.

Adding to 21400243 its reverse (34200412), we get a palindrome (55600655).

The spelling of 21400243 in words is "twenty-one million, four hundred thousand, two hundred forty-three".