21781825 has 12 divisors (see below), whose sum is σ = 29087548. Its totient is φ = 16084800.

The previous prime is 21781807. The next prime is 21781829. The reversal of 21781825 is 52818712.

It can be written as a sum of positive squares in 6 ways, for example, as 6195121 + 15586704 = 2489^2 + 3948^2 .

It is not a de Polignac number, because 21781825 - 2¹⁷ = 21650753 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21781829) 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, 33186 + ... + 33835.

Almost surely, 2^21781825 is an apocalyptic number.

21781825 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

It is an amenable number.

21781825 is a deficient number, since it is larger than the sum of its proper divisors (7305723).

21781825 is a wasteful number, since it uses less digits than its factorization.

21781825 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 67044 (or 67039 counting only the distinct ones).

The product of its digits is 8960, while the sum is 34.

The square root of 21781825 is about 4667.1002774742. The cubic root of 21781825 is about 279.2745890991.

The spelling of 21781825 in words is "twenty-one million, seven hundred eighty-one thousand, eight hundred twenty-five".