21917890 has 16 divisors (see below), whose sum is σ = 39553920. Its totient is φ = 8744560.

The previous prime is 21917867. The next prime is 21917891. The reversal of 21917890 is 9871912.

It is not an unprimeable number, because it can be changed into a prime (21917891) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 1575 + ... + 6805.

It is an arithmetic number, because the mean of its divisors is an integer number (2472120).

Almost surely, 2^21917890 is an apocalyptic number.

21917890 is a deficient number, since it is larger than the sum of its proper divisors (17636030).

21917890 is a wasteful number, since it uses less digits than its factorization.

21917890 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5657.

The product of its (nonzero) digits is 9072, while the sum is 37.

The square root of 21917890 is about 4681.6546220327. The cubic root of 21917890 is about 279.8548993092.

The spelling of 21917890 in words is "twenty-one million, nine hundred seventeen thousand, eight hundred ninety".