21013985 has 4 divisors (see below), whose sum is σ = 25216788. Its totient is φ = 16811184.

The previous prime is 21013961. The next prime is 21013987. The reversal of 21013985 is 58931012.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 3508129 + 17505856 = 1873^2 + 4184^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21013985 is a prime.

It is a super-3 number, since 3×21013985³ (a number of 23 digits) contains 333 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21013987) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2101394 + ... + 2101403.

It is an arithmetic number, because the mean of its divisors is an integer number (6304197).

Almost surely, 2^21013985 is an apocalyptic number.

It is an amenable number.

21013985 is a deficient number, since it is larger than the sum of its proper divisors (4202803).

21013985 is an equidigital number, since it uses as much as digits as its factorization.

21013985 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4202802.

The product of its (nonzero) digits is 2160, while the sum is 29.

The square root of 21013985 is about 4584.1013295956. The cubic root of 21013985 is about 275.9536477855.

Adding to 21013985 its reverse (58931012), we get a palindrome (79944997).

The spelling of 21013985 in words is "twenty-one million, thirteen thousand, nine hundred eighty-five".