18717821 has 2 divisors, whose sum is σ = 18717822. Its totient is φ = 18717820.

The previous prime is 18717817. The next prime is 18717859. The reversal of 18717821 is 12871781.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 18619225 + 98596 = 4315^2 + 314^2 .

It is a cyclic number.

It is not a de Polignac number, because 18717821 - 2² = 18717817 is a prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (18717871) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9358910 + 9358911.

It is an arithmetic number, because the mean of its divisors is an integer number (9358911).

Almost surely, 2^18717821 is an apocalyptic number.

It is an amenable number.

18717821 is a deficient number, since it is larger than the sum of its proper divisors (1).

18717821 is an equidigital number, since it uses as much as digits as its factorization.

18717821 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 6272, while the sum is 35.

The square root of 18717821 is about 4326.4097124521. The cubic root of 18717821 is about 265.5125762027.

The spelling of 18717821 in words is "eighteen million, seven hundred seventeen thousand, eight hundred twenty-one".