21731085 has 20 divisors (see below), whose sum is σ = 38955708. Its totient is φ = 11589696.

The previous prime is 21731081. The next prime is 21731089. The reversal of 21731085 is 58013712.

It is an interprime number because it is at equal distance from previous prime (21731081) and next prime (21731089).

It can be written as a sum of positive squares in 2 ways, for example, as 12257001 + 9474084 = 3501^2 + 3078^2 .

It is not a de Polignac number, because 21731085 - 2² = 21731081 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a zygodrome in base 3.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21731081) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 19 ways as a sum of consecutive naturals, for example, 26424 + ... + 27233.

Almost surely, 2^21731085 is an apocalyptic number.

It is an amenable number.

21731085 is a deficient number, since it is larger than the sum of its proper divisors (17224623).

21731085 is an equidigital number, since it uses as much as digits as its factorization.

21731085 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 53674 (or 53665 counting only the distinct ones).

The product of its (nonzero) digits is 1680, while the sum is 27.

The square root of 21731085 is about 4661.6611845993. The cubic root of 21731085 is about 279.0575670320.

Adding to 21731085 its reverse (58013712), we get a palindrome (79744797).

The spelling of 21731085 in words is "twenty-one million, seven hundred thirty-one thousand, eighty-five".