21755225 has 12 divisors (see below), whose sum is σ = 27060396. Its totient is φ = 17350080.

The previous prime is 21755221. The next prime is 21755243. The reversal of 21755225 is 52255712.

It can be written as a sum of positive squares in 6 ways, for example, as 861184 + 20894041 = 928^2 + 4571^2 .

It is not a de Polignac number, because 21755225 - 2² = 21755221 is a prime.

It is a hoax number, since the sum of its digits (29) coincides with the sum of the digits of its distinct prime factors.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21755221) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 8159 + ... + 10491.

It is an arithmetic number, because the mean of its divisors is an integer number (2255033).

Almost surely, 2^21755225 is an apocalyptic number.

21755225 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

It is an amenable number.

21755225 is a deficient number, since it is larger than the sum of its proper divisors (5305171).

21755225 is a wasteful number, since it uses less digits than its factorization.

21755225 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2716 (or 2711 counting only the distinct ones).

The product of its digits is 7000, while the sum is 29.

The square root of 21755225 is about 4664.2496717050. The cubic root of 21755225 is about 279.1608592639.

Adding to 21755225 its product of digits (7000), we get a square (21762225 = 4665²).

The spelling of 21755225 in words is "twenty-one million, seven hundred fifty-five thousand, two hundred twenty-five".