19660021 has 4 divisors (see below), whose sum is σ = 19801600. Its totient is φ = 19518444.

The previous prime is 19660013. The next prime is 19660027. The reversal of 19660021 is 12006691.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 12006691 = 61 ⋅196831.

It is a cyclic number.

It is not a de Polignac number, because 19660021 - 2³ = 19660013 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (19660027) 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 3 ways as a sum of consecutive naturals, for example, 70581 + ... + 70858.

It is an arithmetic number, because the mean of its divisors is an integer number (4950400).

Almost surely, 2^19660021 is an apocalyptic number.

It is an amenable number.

19660021 is a deficient number, since it is larger than the sum of its proper divisors (141579).

19660021 is a wasteful number, since it uses less digits than its factorization.

19660021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 141578.

The product of its (nonzero) digits is 648, while the sum is 25.

The square root of 19660021 is about 4433.9622235648. The cubic root of 19660021 is about 269.8948882116.

The spelling of 19660021 in words is "nineteen million, six hundred sixty thousand, twenty-one".