21257455 has 4 divisors (see below), whose sum is σ = 25508952. Its totient is φ = 17005960.

The previous prime is 21257419. The next prime is 21257461. The reversal of 21257455 is 55475212.

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

It is not a de Polignac number, because 21257455 - 2¹¹ = 21255407 is a prime.

It is a Smith number, since the sum of its digits (31) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is a plaindrome in base 16.

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, 2125741 + ... + 2125750.

It is an arithmetic number, because the mean of its divisors is an integer number (6377238).

Almost surely, 2^21257455 is an apocalyptic number.

21257455 is a deficient number, since it is larger than the sum of its proper divisors (4251497).

21257455 is an equidigital number, since it uses as much as digits as its factorization.

21257455 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4251496.

The product of its digits is 14000, while the sum is 31.

The square root of 21257455 is about 4610.5807660207. The cubic root of 21257455 is about 277.0152997583.

It can be divided in two parts, 21257 and 455, that added together give a palindrome (21712).

The spelling of 21257455 in words is "twenty-one million, two hundred fifty-seven thousand, four hundred fifty-five".