21787990 has 32 divisors (see below), whose sum is σ = 46370880. Its totient is φ = 7211904.

The previous prime is 21787981. The next prime is 21788017. The reversal of 21787990 is 9978712.

It is a happy number.

It is a congruent number.

It is an unprimeable number.

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 15 ways as a sum of consecutive naturals, for example, 3337 + ... + 7396.

It is an arithmetic number, because the mean of its divisors is an integer number (1449090).

Almost surely, 2^21787990 is an apocalyptic number.

21787990 is an abundant number, since it is smaller than the sum of its proper divisors (24582890).

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

21787990 is a wasteful number, since it uses less digits than its factorization.

21787990 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10776.

The product of its (nonzero) digits is 63504, while the sum is 43.

The square root of 21787990 is about 4667.7607050919. The cubic root of 21787990 is about 279.3009346943.

The spelling of 21787990 in words is "twenty-one million, seven hundred eighty-seven thousand, nine hundred ninety".