21781628 has 12 divisors (see below), whose sum is σ = 41583192. Its totient is φ = 9900720.

The previous prime is 21781609. The next prime is 21781631. The reversal of 21781628 is 82618712.

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 3 ways as a sum of consecutive naturals, for example, 247475 + ... + 247562.

It is an arithmetic number, because the mean of its divisors is an integer number (3465266).

Almost surely, 2^21781628 is an apocalyptic number.

It is an amenable number.

21781628 is a deficient number, since it is larger than the sum of its proper divisors (19801564).

21781628 is a wasteful number, since it uses less digits than its factorization.

21781628 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 495052 (or 495050 counting only the distinct ones).

The product of its digits is 10752, while the sum is 35.

The square root of 21781628 is about 4667.0791722447. The cubic root of 21781628 is about 279.2737471546.

The spelling of 21781628 in words is "twenty-one million, seven hundred eighty-one thousand, six hundred twenty-eight".