21671665 has 8 divisors (see below), whose sum is σ = 26166528. Its totient is φ = 17230320.

The previous prime is 21671633. The next prime is 21671669. The reversal of 21671665 is 56617612.

It is a happy number.

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

It is not a de Polignac number, because 21671665 - 2⁵ = 21671633 is a prime.

It is a super-4 number, since 4×21671665⁴ (a number of 30 digits) contains 4444 as substring. Note that it is a super-d number also for d = 2.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21671665.

It is not an unprimeable number, because it can be changed into a prime (21671669) 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, 12481 + ... + 14110.

It is an arithmetic number, because the mean of its divisors is an integer number (3270816).

Almost surely, 2^21671665 is an apocalyptic number.

It is an amenable number.

21671665 is a deficient number, since it is larger than the sum of its proper divisors (4494863).

21671665 is a wasteful number, since it uses less digits than its factorization.

21671665 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 26759.

The product of its digits is 15120, while the sum is 34.

The square root of 21671665 is about 4655.2835574216. The cubic root of 21671665 is about 278.8029895173.

The spelling of 21671665 in words is "twenty-one million, six hundred seventy-one thousand, six hundred sixty-five".