21517225 has 6 divisors (see below), whose sum is σ = 26681390. Its totient is φ = 17213760.

The previous prime is 21517187. The next prime is 21517231. The reversal of 21517225 is 52271512.

It can be written as a sum of positive squares in 3 ways, for example, as 2742336 + 18774889 = 1656^2 + 4333^2 .

It is not a de Polignac number, because 21517225 - 2²³ = 13128617 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (25), and also a Moran number because the ratio is a prime number: 860689 = 21517225 / (2 + 1 + 5 + 1 + 7 + 2 + 2 + 5).

It is a self number, because there is not a number n which added to its sum of digits gives 21517225.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 430320 + ... + 430369.

Almost surely, 2^21517225 is an apocalyptic number.

21517225 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

It is an amenable number.

21517225 is a deficient number, since it is larger than the sum of its proper divisors (5164165).

21517225 is an equidigital number, since it uses as much as digits as its factorization.

21517225 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 860699 (or 860694 counting only the distinct ones).

The product of its digits is 1400, while the sum is 25.

The square root of 21517225 is about 4638.6662953914. Note that the first 3 decimals coincide. The cubic root of 21517225 is about 278.1391269178.

Adding to 21517225 its reverse (52271512), we get a palindrome (73788737).

The spelling of 21517225 in words is "twenty-one million, five hundred seventeen thousand, two hundred twenty-five".