21204947 has 2 divisors, whose sum is σ = 21204948. Its totient is φ = 21204946.

The previous prime is 21204917. The next prime is 21204949. The reversal of 21204947 is 74940212.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21204947 is a prime.

Together with 21204949, 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 (21204949) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10602473 + 10602474.

It is an arithmetic number, because the mean of its divisors is an integer number (10602474).

Almost surely, 2^21204947 is an apocalyptic number.

21204947 is a deficient number, since it is larger than the sum of its proper divisors (1).

21204947 is an equidigital number, since it uses as much as digits as its factorization.

21204947 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 4032, while the sum is 29.

The square root of 21204947 is about 4604.8829518241. The cubic root of 21204947 is about 276.7870267108.

The spelling of 21204947 in words is "twenty-one million, two hundred four thousand, nine hundred forty-seven".