21978828 has 18 divisors (see below), whose sum is σ = 55557684. Its totient is φ = 7326264.

The previous prime is 21978799. The next prime is 21978871. The reversal of 21978828 is 82887912.

It is a happy number.

It is a tau number, because it is divible by the number of its divisors (18).

It is an unprimeable number.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 305226 + ... + 305297.

It is an arithmetic number, because the mean of its divisors is an integer number (3086538).

Almost surely, 2^21978828 is an apocalyptic number.

It is an amenable number.

21978828 is an abundant number, since it is smaller than the sum of its proper divisors (33578856).

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

21978828 is a wasteful number, since it uses less digits than its factorization.

21978828 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 610533 (or 610528 counting only the distinct ones).

The product of its digits is 129024, while the sum is 45.

The square root of 21978828 is about 4688.1582737787. The cubic root of 21978828 is about 280.1140181904.

It can be divided in two parts, 2197 and 8828, that added together give a square (11025 = 105²).

The spelling of 21978828 in words is "twenty-one million, nine hundred seventy-eight thousand, eight hundred twenty-eight".