19997815 has 4 divisors (see below), whose sum is σ = 23997384. Its totient is φ = 15998248.

The previous prime is 19997807. The next prime is 19997827. The reversal of 19997815 is 51879991.

It is a happy number.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 51879991 = 1193 ⋅43487.

It is a cyclic number.

It is not a de Polignac number, because 19997815 - 2³ = 19997807 is a prime.

It is a Smith number, since the sum of its digits (49) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1999777 + ... + 1999786.

It is an arithmetic number, because the mean of its divisors is an integer number (5999346).

Almost surely, 2^19997815 is an apocalyptic number.

19997815 is a deficient number, since it is larger than the sum of its proper divisors (3999569).

19997815 is an equidigital number, since it uses as much as digits as its factorization.

19997815 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3999568.

The product of its digits is 204120, while the sum is 49.

The square root of 19997815 is about 4471.8916579005. The cubic root of 19997815 is about 271.4318762953.

The spelling of 19997815 in words is "nineteen million, nine hundred ninety-seven thousand, eight hundred fifteen".