19045721 has 4 divisors (see below), whose sum is σ = 19702500. Its totient is φ = 18388944.

The previous prime is 19045717. The next prime is 19045723. The reversal of 19045721 is 12754091.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 12754091 = 7 ⋅1822013.

It can be written as a sum of positive squares in 2 ways, for example, as 9834496 + 9211225 = 3136^2 + 3035^2 .

It is a cyclic number.

It is not a de Polignac number, because 19045721 - 2² = 19045717 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (29), and also a Moran number because the ratio is a prime number: 656749 = 19045721 / (1 + 9 + 0 + 4 + 5 + 7 + 2 + 1).

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (19045723) 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, 328346 + ... + 328403.

It is an arithmetic number, because the mean of its divisors is an integer number (4925625).

Almost surely, 2^19045721 is an apocalyptic number.

It is an amenable number.

19045721 is a deficient number, since it is larger than the sum of its proper divisors (656779).

19045721 is an equidigital number, since it uses as much as digits as its factorization.

19045721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 656778.

The product of its (nonzero) digits is 2520, while the sum is 29.

The square root of 19045721 is about 4364.1403506304. The cubic root of 19045721 is about 267.0540319982.

The spelling of 19045721 in words is "nineteen million, forty-five thousand, seven hundred twenty-one".