19947209 has 2 divisors, whose sum is σ = 19947210. Its totient is φ = 19947208.

The previous prime is 19947203. The next prime is 19947247. The reversal of 19947209 is 90274991.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 16605625 + 3341584 = 4075^2 + 1828^2 .

It is an emirp because it is prime and its reverse (90274991) is a distict prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-19947209 is a prime.

It is a super-2 number, since 2×19947209² = 795782293779362, which contains 22 as substring.

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 (19947203) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9973604 + 9973605.

It is an arithmetic number, because the mean of its divisors is an integer number (9973605).

Almost surely, 2^19947209 is an apocalyptic number.

It is an amenable number.

19947209 is a deficient number, since it is larger than the sum of its proper divisors (1).

19947209 is an equidigital number, since it uses as much as digits as its factorization.

19947209 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 40824, while the sum is 41.

The square root of 19947209 is about 4466.2298418241. The cubic root of 19947209 is about 271.2027231840.

The spelling of 19947209 in words is "nineteen million, nine hundred forty-seven thousand, two hundred nine".