19996021 has 4 divisors (see below), whose sum is σ = 20536492. Its totient is φ = 19455552.

The previous prime is 19996019. The next prime is 19996049. The reversal of 19996021 is 12069991.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 12069991 = 397 ⋅30403.

It can be written as a sum of positive squares in 2 ways, for example, as 16719921 + 3276100 = 4089^2 + 1810^2 .

It is a cyclic number.

It is not a de Polignac number, because 19996021 - 2¹ = 19996019 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (37), and also a Moran number because the ratio is a prime number: 540433 = 19996021 / (1 + 9 + 9 + 9 + 6 + 0 + 2 + 1).

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (19996001) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 270180 + ... + 270253.

It is an arithmetic number, because the mean of its divisors is an integer number (5134123).

Almost surely, 2^19996021 is an apocalyptic number.

It is an amenable number.

19996021 is a deficient number, since it is larger than the sum of its proper divisors (540471).

19996021 is an equidigital number, since it uses as much as digits as its factorization.

19996021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 540470.

The product of its (nonzero) digits is 8748, while the sum is 37.

The square root of 19996021 is about 4471.6910671467. The cubic root of 19996021 is about 271.4237593528.

The spelling of 19996021 in words is "nineteen million, nine hundred ninety-six thousand, twenty-one".