21012665 has 8 divisors (see below), whose sum is σ = 25272000. Its totient is φ = 16772272.

The previous prime is 21012661. The next prime is 21012671. The reversal of 21012665 is 56621012.

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

It is a cyclic number.

It is not a de Polignac number, because 21012665 - 2² = 21012661 is a prime.

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 21012665.

It is not an unprimeable number, because it can be changed into a prime (21012661) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 2165 + ... + 6834.

It is an arithmetic number, because the mean of its divisors is an integer number (3159000).

Almost surely, 2^21012665 is an apocalyptic number.

It is an amenable number.

21012665 is a deficient number, since it is larger than the sum of its proper divisors (4259335).

21012665 is an equidigital number, since it uses as much as digits as its factorization.

21012665 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9471.

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

The square root of 21012665 is about 4583.9573514595. The cubic root of 21012665 is about 275.9478696264.

Adding to 21012665 its reverse (56621012), we get a palindrome (77633677).

The spelling of 21012665 in words is "twenty-one million, twelve thousand, six hundred sixty-five".