19991247 has 4 divisors (see below), whose sum is σ = 26655000. Its totient is φ = 13327496.

The previous prime is 19991243. The next prime is 19991267. The reversal of 19991247 is 74219991.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 74219991 = 3 ⋅24739997.

It is a cyclic number.

It is not a de Polignac number, because 19991247 - 2² = 19991243 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 19991199 and 19991208.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (19991243) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3331872 + ... + 3331877.

It is an arithmetic number, because the mean of its divisors is an integer number (6663750).

Almost surely, 2^19991247 is an apocalyptic number.

19991247 is a deficient number, since it is larger than the sum of its proper divisors (6663753).

19991247 is an equidigital number, since it uses as much as digits as its factorization.

19991247 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6663752.

The product of its digits is 40824, while the sum is 42.

The square root of 19991247 is about 4471.1572327531. The cubic root of 19991247 is about 271.4021570523.

The spelling of 19991247 in words is "nineteen million, nine hundred ninety-one thousand, two hundred forty-seven".