21678724 has 24 divisors (see below), whose sum is σ = 39019680. Its totient is φ = 10534656.

The previous prime is 21678697. The next prime is 21678731. The reversal of 21678724 is 42787612.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 22419 + ... + 23365.

It is an arithmetic number, because the mean of its divisors is an integer number (1625820).

Almost surely, 2^21678724 is an apocalyptic number.

It is an amenable number.

21678724 is a deficient number, since it is larger than the sum of its proper divisors (17340956).

21678724 is a wasteful number, since it uses less digits than its factorization.

21678724 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1107 (or 1105 counting only the distinct ones).

The product of its digits is 37632, while the sum is 37.

The square root of 21678724 is about 4656.0416664802. The cubic root of 21678724 is about 278.8332572526.

It can be divided in two parts, 216787 and 24, that added together give a triangular number (216811 = T₆₅₈).

The spelling of 21678724 in words is "twenty-one million, six hundred seventy-eight thousand, seven hundred twenty-four".