21507705 has 24 divisors (see below), whose sum is σ = 38567880. Its totient is φ = 11074560.

The previous prime is 21507701. The next prime is 21507709. The reversal of 21507705 is 50770512.

It is an interprime number because it is at equal distance from previous prime (21507701) and next prime (21507709).

It can be written as a sum of positive squares in 4 ways, for example, as 1687401 + 19820304 = 1299^2 + 4452^2 .

It is not a de Polignac number, because 21507705 - 2² = 21507701 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21507701) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 6936 + ... + 9545.

It is an arithmetic number, because the mean of its divisors is an integer number (1606995).

Almost surely, 2^21507705 is an apocalyptic number.

It is an amenable number.

21507705 is a deficient number, since it is larger than the sum of its proper divisors (17060175).

21507705 is a wasteful number, since it uses less digits than its factorization.

21507705 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 16521 (or 16518 counting only the distinct ones).

The product of its (nonzero) digits is 2450, while the sum is 27.

The square root of 21507705 is about 4637.6400248402. The cubic root of 21507705 is about 278.0981012575.

The spelling of 21507705 in words is "twenty-one million, five hundred seven thousand, seven hundred five".