19998521 has 2 divisors, whose sum is σ = 19998522. Its totient is φ = 19998520.

The previous prime is 19998497. The next prime is 19998533. The reversal of 19998521 is 12589991.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 16974400 + 3024121 = 4120^2 + 1739^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-19998521 is a prime.

It is a Sophie Germain prime.

It is a Chen prime.

It is a Curzon number.

It is not a weakly prime, because it can be changed into another prime (19998541) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9999260 + 9999261.

It is an arithmetic number, because the mean of its divisors is an integer number (9999261).

Almost surely, 2^19998521 is an apocalyptic number.

It is an amenable number.

19998521 is a deficient number, since it is larger than the sum of its proper divisors (1).

19998521 is an equidigital number, since it uses as much as digits as its factorization.

19998521 is an evil number, because the sum of its binary digits is even.

The product of its digits is 58320, while the sum is 44.

The square root of 19998521 is about 4471.9705947155. The cubic root of 19998521 is about 271.4350704551.

The spelling of 19998521 in words is "nineteen million, nine hundred ninety-eight thousand, five hundred twenty-one".