21813778 has 16 divisors (see below), whose sum is σ = 37767744. Its totient is φ = 9255600.

The previous prime is 21813761. The next prime is 21813809. The reversal of 21813778 is 87731812.

It is an unprimeable number.

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, 6300 + ... + 9127.

It is an arithmetic number, because the mean of its divisors is an integer number (2360484).

Almost surely, 2^21813778 is an apocalyptic number.

21813778 is a deficient number, since it is larger than the sum of its proper divisors (15953966).

21813778 is a wasteful number, since it uses less digits than its factorization.

21813778 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 15537.

The product of its digits is 18816, while the sum is 37.

The square root of 21813778 is about 4670.5222406065. The cubic root of 21813778 is about 279.4110836453.

The spelling of 21813778 in words is "twenty-one million, eight hundred thirteen thousand, seven hundred seventy-eight".