21365661 has 8 divisors (see below), whose sum is σ = 28512640. Its totient is φ = 14231232.

The previous prime is 21365657. The next prime is 21365699. The reversal of 21365661 is 16656312.

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

It is not a de Polignac number, because 21365661 - 2² = 21365657 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21365621) 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 in 7 ways as a sum of consecutive naturals, for example, 2076 + ... + 6858.

It is an arithmetic number, because the mean of its divisors is an integer number (3564080).

Almost surely, 2^21365661 is an apocalyptic number.

It is an amenable number.

21365661 is a deficient number, since it is larger than the sum of its proper divisors (7146979).

21365661 is a wasteful number, since it uses less digits than its factorization.

21365661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6275.

The product of its digits is 6480, while the sum is 30.

The square root of 21365661 is about 4622.3004013153. The cubic root of 21365661 is about 277.4845312374.

The spelling of 21365661 in words is "twenty-one million, three hundred sixty-five thousand, six hundred sixty-one".