21000825 has 18 divisors (see below), whose sum is σ = 37615214. Its totient is φ = 11200320.

The previous prime is 21000823. The next prime is 21000827. The reversal of 21000825 is 52800012.

It is an interprime number because it is at equal distance from previous prime (21000823) and next prime (21000827).

It can be written as a sum of positive squares in 3 ways, for example, as 831744 + 20169081 = 912^2 + 4491^2 .

It is not a de Polignac number, because 21000825 - 2¹ = 21000823 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a junction number, because it is equal to n+sod(n) for n = 21000798 and 21000807.

It is not an unprimeable number, because it can be changed into a prime (21000821) 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 17 ways as a sum of consecutive naturals, for example, 46444 + ... + 46893.

Almost surely, 2^21000825 is an apocalyptic number.

21000825 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

It is an amenable number.

21000825 is a deficient number, since it is larger than the sum of its proper divisors (16614389).

21000825 is a wasteful number, since it uses less digits than its factorization.

21000825 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 93353 (or 93345 counting only the distinct ones).

The product of its (nonzero) digits is 160, while the sum is 18.

The square root of 21000825 is about 4582.6657089515. The cubic root of 21000825 is about 275.8960304677.

Adding to 21000825 its reverse (52800012), we get a palindrome (73800837).

The spelling of 21000825 in words is "twenty-one million, eight hundred twenty-five", and thus it is an aban number.