21978000 has 320 divisors, whose sum is σ = 88208640. Its totient is φ = 5184000.

The previous prime is 21977993. The next prime is 21978007. The reversal of 21978000 is 87912.

It is an interprime number because it is at equal distance from previous prime (21977993) and next prime (21978007).

It is a Harshad number since it is a multiple of its sum of digits (27).

It is not an unprimeable number, because it can be changed into a prime (21978007) by changing a digit.

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 63 ways as a sum of consecutive naturals, for example, 593982 + ... + 594018.

It is an arithmetic number, because the mean of its divisors is an integer number (275652).

Almost surely, 2^21978000 is an apocalyptic number.

21978000 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 21978000, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (44104320).

21978000 is an abundant number, since it is smaller than the sum of its proper divisors (66230640).

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

21978000 is a wasteful number, since it uses less digits than its factorization.

21978000 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 80 (or 58 counting only the distinct ones).

The product of its (nonzero) digits is 1008, while the sum is 27.

The square root of 21978000 is about 4688.0699653482. The cubic root of 21978000 is about 280.1105006034.

It can be divided in two parts, 2197 and 8000, that multiplied together give a cube (17576000 = 260³).

The spelling of 21978000 in words is "twenty-one million, nine hundred seventy-eight thousand".