21605013 has 6 divisors (see below), whose sum is σ = 31207254. Its totient is φ = 14403336.

The previous prime is 21605009. The next prime is 21605039. The reversal of 21605013 is 31050612.

21605013 is a `hidden beast` number, since 2 + 160 + 501 + 3 = 666.

It can be written as a sum of positive squares in only one way, i.e., 21594609 + 10404 = 4647^2 + 102^2 .

It is not a de Polignac number, because 21605013 - 2² = 21605009 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21605053) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 1200270 + ... + 1200287.

It is an arithmetic number, because the mean of its divisors is an integer number (5201209).

Almost surely, 2^21605013 is an apocalyptic number.

It is an amenable number.

21605013 is a deficient number, since it is larger than the sum of its proper divisors (9602241).

21605013 is a wasteful number, since it uses less digits than its factorization.

21605013 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2400563 (or 2400560 counting only the distinct ones).

The product of its (nonzero) digits is 180, while the sum is 18.

The square root of 21605013 is about 4648.1192970921. The cubic root of 21605013 is about 278.5168730584.

Adding to 21605013 its reverse (31050612), we get a palindrome (52655625).

The spelling of 21605013 in words is "twenty-one million, six hundred five thousand, thirteen".