21390451 has 4 divisors (see below), whose sum is σ = 21402304. Its totient is φ = 21378600.

The previous prime is 21390449. The next prime is 21390461. The reversal of 21390451 is 15409312.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is not a de Polignac number, because 21390451 - 2¹ = 21390449 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21390461) 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, 2595 + ... + 7036.

It is an arithmetic number, because the mean of its divisors is an integer number (5350576).

Almost surely, 2^21390451 is an apocalyptic number.

21390451 is a deficient number, since it is larger than the sum of its proper divisors (11853).

21390451 is an equidigital number, since it uses as much as digits as its factorization.

21390451 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 11852.

The product of its (nonzero) digits is 1080, while the sum is 25.

The square root of 21390451 is about 4624.9811891509. The cubic root of 21390451 is about 277.5918090292.

Adding to 21390451 its reverse (15409312), we get a palindrome (36799763).

The spelling of 21390451 in words is "twenty-one million, three hundred ninety thousand, four hundred fifty-one".