21771240 has 64 divisors (see below), whose sum is σ = 65620800. Its totient is φ = 5778432.

The previous prime is 21771221. The next prime is 21771247. The reversal of 21771240 is 4217712.

It is a super-2 number, since 2×21771240² = 947973782275200, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (24).

It is a self number, because there is not a number n which added to its sum of digits gives 21771240.

It is not an unprimeable number, because it can be changed into a prime (21771247) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 50064 + ... + 50496.

It is an arithmetic number, because the mean of its divisors is an integer number (1025325).

Almost surely, 2^21771240 is an apocalyptic number.

21771240 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21771240 is an abundant number, since it is smaller than the sum of its proper divisors (43849560).

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

21771240 is a wasteful number, since it uses less digits than its factorization.

21771240 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 866 (or 862 counting only the distinct ones).

The product of its (nonzero) digits is 784, while the sum is 24.

The square root of 21771240 is about 4665.9661378968. The cubic root of 21771240 is about 279.2293434183.

Adding to 21771240 its reverse (4217712), we get a palindrome (25988952).

The spelling of 21771240 in words is "twenty-one million, seven hundred seventy-one thousand, two hundred forty".