18628721 has 4 divisors (see below), whose sum is σ = 19609200. Its totient is φ = 17648244.

The previous prime is 18628717. The next prime is 18628733. The reversal of 18628721 is 12782681.

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: 12782681 = 167 ⋅76543.

It is a cyclic number.

It is not a de Polignac number, because 18628721 - 2² = 18628717 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (18628021) 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, 490211 + ... + 490248.

It is an arithmetic number, because the mean of its divisors is an integer number (4902300).

Almost surely, 2^18628721 is an apocalyptic number.

It is an amenable number.

18628721 is a deficient number, since it is larger than the sum of its proper divisors (980479).

18628721 is an equidigital number, since it uses as much as digits as its factorization.

18628721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 980478.

The product of its digits is 10752, while the sum is 35.

The square root of 18628721 is about 4316.1002073631. The cubic root of 18628721 is about 265.0906109981.

The spelling of 18628721 in words is "eighteen million, six hundred twenty-eight thousand, seven hundred twenty-one".