21979800 has 72 divisors (see below), whose sum is σ = 73821540. Its totient is φ = 5860800.

The previous prime is 21979787. The next prime is 21979807. The reversal of 21979800 is 897912.

It is a happy number.

It is a tau number, because it is divible by the number of its divisors (72).

It is a super-2 number, since 2×21979800² = 966223216080000, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21979807) by changing a digit.

It is a polite number, since it can be written in 17 ways as a sum of consecutive naturals, for example, 4306 + ... + 7905.

Almost surely, 2^21979800 is an apocalyptic number.

21979800 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21979800 is an abundant number, since it is smaller than the sum of its proper divisors (51841740).

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

21979800 is a wasteful number, since it uses less digits than its factorization.

21979800 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 12233 (or 12221 counting only the distinct ones).

The product of its (nonzero) digits is 9072, while the sum is 36.

The square root of 21979800 is about 4688.2619380747. The cubic root of 21979800 is about 280.1181474190.

The spelling of 21979800 in words is "twenty-one million, nine hundred seventy-nine thousand, eight hundred".