21287225 has 12 divisors (see below), whose sum is σ = 26575680. Its totient is φ = 16914000.

The previous prime is 21287221. The next prime is 21287243. The reversal of 21287225 is 52278212.

It is not a de Polignac number, because 21287225 - 2² = 21287221 is a prime.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21287221) by changing a digit.

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 11 ways as a sum of consecutive naturals, for example, 956 + ... + 6594.

It is an arithmetic number, because the mean of its divisors is an integer number (2214640).

Almost surely, 2^21287225 is an apocalyptic number.

21287225 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

It is an amenable number.

21287225 is a deficient number, since it is larger than the sum of its proper divisors (5288455).

21287225 is a wasteful number, since it uses less digits than its factorization.

21287225 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5800 (or 5795 counting only the distinct ones).

The product of its digits is 4480, while the sum is 29.

The square root of 21287225 is about 4613.8080801004. The cubic root of 21287225 is about 277.1445547852.

It can be divided in two parts, 21287 and 225, that added together give a palindrome (21512).

The spelling of 21287225 in words is "twenty-one million, two hundred eighty-seven thousand, two hundred twenty-five".