21206545 has 8 divisors (see below), whose sum is σ = 25560360. Its totient is φ = 16890240.

The previous prime is 21206533. The next prime is 21206557. The reversal of 21206545 is 54560212.

It is an interprime number because it is at equal distance from previous prime (21206533) and next prime (21206557).

It can be written as a sum of positive squares in 4 ways, for example, as 13786369 + 7420176 = 3713^2 + 2724^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21206545 - 2¹¹ = 21204497 is a prime.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 8116 + ... + 10405.

It is an arithmetic number, because the mean of its divisors is an integer number (3195045).

Almost surely, 2^21206545 is an apocalyptic number.

It is an amenable number.

21206545 is a deficient number, since it is larger than the sum of its proper divisors (4353815).

21206545 is a wasteful number, since it uses less digits than its factorization.

21206545 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 18755.

The product of its (nonzero) digits is 2400, while the sum is 25.

The square root of 21206545 is about 4605.0564600230. The cubic root of 21206545 is about 276.7939794053.

Adding to 21206545 its reverse (54560212), we get a palindrome (75766757).

The spelling of 21206545 in words is "twenty-one million, two hundred six thousand, five hundred forty-five".