21678740 has 24 divisors (see below), whose sum is σ = 48204072. Its totient is φ = 8161280.

The previous prime is 21678733. The next prime is 21678763. The reversal of 21678740 is 4787612.

It is a happy number.

It can be written as a sum of positive squares in 4 ways, for example, as 6948496 + 14730244 = 2636^2 + 3838^2 .

It is a self number, because there is not a number n which added to its sum of digits gives 21678740.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 31541 + ... + 32220.

It is an arithmetic number, because the mean of its divisors is an integer number (2008503).

Almost surely, 2^21678740 is an apocalyptic number.

21678740 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21678740 is an abundant number, since it is smaller than the sum of its proper divisors (26525332).

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

21678740 is a wasteful number, since it uses less digits than its factorization.

21678740 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 63787 (or 63785 counting only the distinct ones).

The product of its (nonzero) digits is 18816, while the sum is 35.

The square root of 21678740 is about 4656.0433846776. The cubic root of 21678740 is about 278.8333258503.

The spelling of 21678740 in words is "twenty-one million, six hundred seventy-eight thousand, seven hundred forty".