21987947 has 2 divisors, whose sum is σ = 21987948. Its totient is φ = 21987946.

The previous prime is 21987929. The next prime is 21987967. The reversal of 21987947 is 74978912.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21987947 - 2¹⁴ = 21971563 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21987907) 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, 10993973 + 10993974.

It is an arithmetic number, because the mean of its divisors is an integer number (10993974).

Almost surely, 2^21987947 is an apocalyptic number.

21987947 is a deficient number, since it is larger than the sum of its proper divisors (1).

21987947 is an equidigital number, since it uses as much as digits as its factorization.

21987947 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 254016, while the sum is 47.

The square root of 21987947 is about 4689.1307296769. The cubic root of 21987947 is about 280.1527525359.

The spelling of 21987947 in words is "twenty-one million, nine hundred eighty-seven thousand, nine hundred forty-seven".