21779916 has 12 divisors (see below), whose sum is σ = 50819832. Its totient is φ = 7259968.

The previous prime is 21779903. The next prime is 21779917. The reversal of 21779916 is 61997712.

It is a happy number.

It is a tau number, because it is divible by the number of its divisors (12).

It is a Smith number, since the sum of its digits (42) coincides with the sum of the digits of its prime factors.

It is not an unprimeable number, because it can be changed into a prime (21779917) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 907485 + ... + 907508.

It is an arithmetic number, because the mean of its divisors is an integer number (4234986).

Almost surely, 2^21779916 is an apocalyptic number.

It is an amenable number.

21779916 is an abundant number, since it is smaller than the sum of its proper divisors (29039916).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21779916 is a wasteful number, since it uses less digits than its factorization.

21779916 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1815000 (or 1814998 counting only the distinct ones).

The product of its digits is 47628, while the sum is 42.

The square root of 21779916 is about 4666.8957562817. The cubic root of 21779916 is about 279.2664301445.

The spelling of 21779916 in words is "twenty-one million, seven hundred seventy-nine thousand, nine hundred sixteen".