21201566 has 4 divisors (see below), whose sum is σ = 31802352. Its totient is φ = 10600782.

The previous prime is 21201563. The next prime is 21201569. The reversal of 21201566 is 66510212.

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

It is an interprime number because it is at equal distance from previous prime (21201563) and next prime (21201569).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21201563) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5300390 + ... + 5300393.

It is an arithmetic number, because the mean of its divisors is an integer number (7950588).

Almost surely, 2^21201566 is an apocalyptic number.

21201566 is a deficient number, since it is larger than the sum of its proper divisors (10600786).

21201566 is a wasteful number, since it uses less digits than its factorization.

21201566 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10600785.

The product of its (nonzero) digits is 720, while the sum is 23.

The square root of 21201566 is about 4604.5158268813. The cubic root of 21201566 is about 276.7723152588.

Adding to 21201566 its reverse (66510212), we get a palindrome (87711778).

The spelling of 21201566 in words is "twenty-one million, two hundred one thousand, five hundred sixty-six".