21147665 has 64 divisors (see below), whose sum is σ = 34560000. Its totient is φ = 12277440.

The previous prime is 21147661. The next prime is 21147667. The reversal of 21147665 is 56674112.

It is not a de Polignac number, because 21147665 - 2² = 21147661 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21147661) by changing a digit.

It is a polite number, since it can be written in 63 ways as a sum of consecutive naturals, for example, 358406 + ... + 358464.

It is an arithmetic number, because the mean of its divisors is an integer number (540000).

Almost surely, 2^21147665 is an apocalyptic number.

It is an amenable number.

21147665 is a deficient number, since it is larger than the sum of its proper divisors (13412335).

21147665 is a wasteful number, since it uses less digits than its factorization.

21147665 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 115 (or 101 counting only the distinct ones).

The product of its digits is 10080, while the sum is 32.

The square root of 21147665 is about 4598.6590436778. The cubic root of 21147665 is about 276.5375690019.

It can be divided in two parts, 21147 and 665, that added together give a palindrome (21812).

The spelling of 21147665 in words is "twenty-one million, one hundred forty-seven thousand, six hundred sixty-five".