21978500 has 48 divisors (see below), whose sum is σ = 48550320. Its totient is φ = 8691200.

The previous prime is 21978487. The next prime is 21978521. The reversal of 21978500 is 587912.

21978500 = T₉ + T₁₀ + ... + T₅₀₈.

It can be written as a sum of positive squares in 8 ways, for example, as 16924996 + 5053504 = 4114^2 + 2248^2 .

It is a hoax number, since the sum of its digits (32) coincides with the sum of the digits of its distinct prime factors.

It is a congruent number.

It is an unprimeable number.

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 15 ways as a sum of consecutive naturals, for example, 56306 + ... + 56694.

It is an arithmetic number, because the mean of its divisors is an integer number (1011465).

Almost surely, 2^21978500 is an apocalyptic number.

21978500 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21978500, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (24275160).

21978500 is an abundant number, since it is smaller than the sum of its proper divisors (26571820).

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

21978500 is a wasteful number, since it uses less digits than its factorization.

21978500 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 521 (or 509 counting only the distinct ones).

The product of its (nonzero) digits is 5040, while the sum is 32.

The square root of 21978500 is about 4688.1232918941. The cubic root of 21978500 is about 280.1126247608.

The spelling of 21978500 in words is "twenty-one million, nine hundred seventy-eight thousand, five hundred".