21665001 has 24 divisors (see below), whose sum is σ = 30993664. Its totient is φ = 13446720.

The previous prime is 21664967. The next prime is 21665009. The reversal of 21665001 is 10056612.

It is a happy number.

It is not a de Polignac number, because 21665001 - 2¹⁰ = 21663977 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21665009) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 78075 + ... + 78351.

Almost surely, 2^21665001 is an apocalyptic number.

It is an amenable number.

21665001 is a deficient number, since it is larger than the sum of its proper divisors (9328663).

21665001 is a wasteful number, since it uses less digits than its factorization.

21665001 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 369 (or 340 counting only the distinct ones).

The product of its (nonzero) digits is 360, while the sum is 21.

The square root of 21665001 is about 4654.5677565162. The cubic root of 21665001 is about 278.7744094399.

The spelling of 21665001 in words is "twenty-one million, six hundred sixty-five thousand, one".