21665502001 has 24 divisors (see below), whose sum is σ = 26863389504. Its totient is φ = 17223913440.

The previous prime is 21665501999. The next prime is 21665502007. The reversal of 21665502001 is 10020556612.

It is not a de Polignac number, because 21665502001 - 2¹ = 21665501999 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21665502007) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 158221 + ... + 261466.

It is an arithmetic number, because the mean of its divisors is an integer number (1119307896).

Almost surely, 2^21665502001 is an apocalyptic number.

It is an amenable number.

21665502001 is a deficient number, since it is larger than the sum of its proper divisors (5197887503).

21665502001 is a wasteful number, since it uses less digits than its factorization.

21665502001 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 419749 (or 419730 counting only the distinct ones).

The product of its (nonzero) digits is 3600, while the sum is 28.

The spelling of 21665502001 in words is "twenty-one billion, six hundred sixty-five million, five hundred two thousand, one".