19664021 has 16 divisors (see below), whose sum is σ = 21800688. Its totient is φ = 17625600.

The previous prime is 19664009. The next prime is 19664063. The reversal of 19664021 is 12046691.

It can be written as a sum of positive squares in 8 ways, for example, as 9991921 + 9672100 = 3161^2 + 3110^2 .

It is a cyclic number.

It is not a de Polignac number, because 19664021 - 2¹⁴ = 19647637 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (19664081) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 108551 + ... + 108731.

It is an arithmetic number, because the mean of its divisors is an integer number (1362543).

Almost surely, 2^19664021 is an apocalyptic number.

It is an amenable number.

19664021 is a deficient number, since it is larger than the sum of its proper divisors (2136667).

19664021 is a wasteful number, since it uses less digits than its factorization.

19664021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 392.

The product of its (nonzero) digits is 2592, while the sum is 29.

The square root of 19664021 is about 4434.4132644579. The cubic root of 19664021 is about 269.9131911142.

The spelling of 19664021 in words is "nineteen million, six hundred sixty-four thousand, twenty-one".