21009455 has 4 divisors (see below), whose sum is σ = 25211352. Its totient is φ = 16807560.

The previous prime is 21009449. The next prime is 21009491. The reversal of 21009455 is 55490012.

It is a semiprime because it is the product of two primes.

It is not a de Polignac number, because 21009455 - 2⁸ = 21009199 is a prime.

It is a Duffinian number.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2100941 + ... + 2100950.

It is an arithmetic number, because the mean of its divisors is an integer number (6302838).

Almost surely, 2^21009455 is an apocalyptic number.

21009455 is a deficient number, since it is larger than the sum of its proper divisors (4201897).

21009455 is an equidigital number, since it uses as much as digits as its factorization.

21009455 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4201896.

The product of its (nonzero) digits is 1800, while the sum is 26.

The square root of 21009455 is about 4583.6072039388. The cubic root of 21009455 is about 275.9338171844.

Adding to 21009455 its reverse (55490012), we get a palindrome (76499467).

The spelling of 21009455 in words is "twenty-one million, nine thousand, four hundred fifty-five".