21221947 has 2 divisors, whose sum is σ = 21221948. Its totient is φ = 21221946.

The previous prime is 21221929. The next prime is 21221953. The reversal of 21221947 is 74912212.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21221947 - 2¹⁹ = 20697659 is a prime.

It is not a weakly prime, because it can be changed into another prime (21221927) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10610973 + 10610974.

It is an arithmetic number, because the mean of its divisors is an integer number (10610974).

Almost surely, 2^21221947 is an apocalyptic number.

21221947 is a deficient number, since it is larger than the sum of its proper divisors (1).

21221947 is an equidigital number, since it uses as much as digits as its factorization.

21221947 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 2016, while the sum is 28.

The square root of 21221947 is about 4606.7284486933. The cubic root of 21221947 is about 276.8609736469.

The spelling of 21221947 in words is "twenty-one million, two hundred twenty-one thousand, nine hundred forty-seven".