21780000 has 270 divisors, whose sum is σ = 85071987. Its totient is φ = 5280000.

The previous prime is 21779987. The next prime is 21780001. The reversal of 21780000 is 8712.

It is a powerful number, because all its prime factors have an exponent greater than 1 and also an Achilles number because it is not a perfect power.

It can be written as a sum of positive squares in 3 ways, for example, as 5035536 + 16744464 = 2244^2 + 4092^2 .

It is an ABA number since it can be written as A⋅B^A, here for A=2, B=3300.

It is a Harshad number since it is a multiple of its sum of digits (18).

It is not an unprimeable number, because it can be changed into a prime (21780001) by changing a digit.

It is a polite number, since it can be written in 44 ways as a sum of consecutive naturals, for example, 1979995 + ... + 1980005.

Almost surely, 2^21780000 is an apocalyptic number.

21780000 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 21780000

21780000 is an abundant number, since it is smaller than the sum of its proper divisors (63291987).

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

21780000 is a wasteful number, since it uses less digits than its factorization.

21780000 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 58 (or 21 counting only the distinct ones).

The product of its (nonzero) digits is 112, while the sum is 18.

The square root of 21780000 is about 4666.9047558312. The cubic root of 21780000 is about 279.2667891656.

Multiplying 21780000 by its sum of digits (18), we get a square (392040000 = 19800²).

21780000 divided by its sum of digits (18) gives a square (1210000 = 1100²).

Adding to 21780000 its reverse (8712), we get a palindrome (21788712).

Multiplying 21780000 by its reverse (8712), we get a 4-th power (189747360000 = 660⁴).

21780000 divided by its reverse (8712) gives a square (2500 = 50²).

The spelling of 21780000 in words is "twenty-one million, seven hundred eighty thousand".