21899947 has 4 divisors (see below), whose sum is σ = 21909456. Its totient is φ = 21890440.

The previous prime is 21899939. The next prime is 21899987. The reversal of 21899947 is 74999812.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is not a de Polignac number, because 21899947 - 2³ = 21899939 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21899947.

It is not an unprimeable number, because it can be changed into a prime (21899987) 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 in 3 ways as a sum of consecutive naturals, for example, 1122 + ... + 6712.

It is an arithmetic number, because the mean of its divisors is an integer number (5477364).

Almost surely, 2^21899947 is an apocalyptic number.

21899947 is a deficient number, since it is larger than the sum of its proper divisors (9509).

21899947 is an equidigital number, since it uses as much as digits as its factorization.

21899947 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9508.

The product of its digits is 326592, while the sum is 49.

The square root of 21899947 is about 4679.7379200122. The cubic root of 21899947 is about 279.7785110659.

The spelling of 21899947 in words is "twenty-one million, eight hundred ninety-nine thousand, nine hundred forty-seven".