18670721 has 2 divisors, whose sum is σ = 18670722. Its totient is φ = 18670720.

The previous prime is 18670669. The next prime is 18670723. The reversal of 18670721 is 12707681.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 10491121 + 8179600 = 3239^2 + 2860^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-18670721 is a prime.

Together with 18670723, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (18670723) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9335360 + 9335361.

It is an arithmetic number, because the mean of its divisors is an integer number (9335361).

Almost surely, 2^18670721 is an apocalyptic number.

It is an amenable number.

18670721 is a deficient number, since it is larger than the sum of its proper divisors (1).

18670721 is an equidigital number, since it uses as much as digits as its factorization.

18670721 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 4704, while the sum is 32.

The square root of 18670721 is about 4320.9629713757. The cubic root of 18670721 is about 265.2896844031.

It can be divided in two parts, 18670 and 721, that added together give a palindrome (19391).

The spelling of 18670721 in words is "eighteen million, six hundred seventy thousand, seven hundred twenty-one".