21566740 has 48 divisors (see below), whose sum is σ = 49286160. Its totient is φ = 7879680.

The previous prime is 21566737. The next prime is 21566771. The reversal of 21566740 is 4766512.

It is a happy number.

It can be written as a sum of positive squares in 8 ways, for example, as 5550736 + 16016004 = 2356^2 + 4002^2 .

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 27960 + ... + 28720.

It is an arithmetic number, because the mean of its divisors is an integer number (1026795).

Almost surely, 2^21566740 is an apocalyptic number.

21566740 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 21566740, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (24643080).

21566740 is an abundant number, since it is smaller than the sum of its proper divisors (27719420).

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

21566740 is a wasteful number, since it uses less digits than its factorization.

21566740 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 892 (or 890 counting only the distinct ones).

The product of its (nonzero) digits is 10080, while the sum is 31.

The square root of 21566740 is about 4644.0004306632. Note that the first 3 decimals coincide. The cubic root of 21566740 is about 278.3523128400.

The spelling of 21566740 in words is "twenty-one million, five hundred sixty-six thousand, seven hundred forty".