21251457 has 8 divisors (see below), whose sum is σ = 31483680. Its totient is φ = 14167620.

The previous prime is 21251453. The next prime is 21251467. The reversal of 21251457 is 75415212.

It is not a de Polignac number, because 21251457 - 2² = 21251453 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (27), and also a Moran number because the ratio is a prime number: 787091 = 21251457 / (2 + 1 + 2 + 5 + 1 + 4 + 5 + 7).

It is a self number, because there is not a number n which added to its sum of digits gives 21251457.

It is not an unprimeable number, because it can be changed into a prime (21251453) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 393519 + ... + 393572.

It is an arithmetic number, because the mean of its divisors is an integer number (3935460).

Almost surely, 2^21251457 is an apocalyptic number.

21251457 is a gapful number since it is divisible by the number (27) formed by its first and last digit.

It is an amenable number.

21251457 is a deficient number, since it is larger than the sum of its proper divisors (10232223).

21251457 is an equidigital number, since it uses as much as digits as its factorization.

21251457 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 787100 (or 787094 counting only the distinct ones).

The product of its digits is 2800, while the sum is 27.

The square root of 21251457 is about 4609.9302597762. The cubic root of 21251457 is about 276.9892431104.

Adding to 21251457 its reverse (75415212), we get a palindrome (96666669).

The spelling of 21251457 in words is "twenty-one million, two hundred fifty-one thousand, four hundred fifty-seven".