21681748 has 18 divisors (see below), whose sum is σ = 41706938. Its totient is φ = 9855120.

The previous prime is 21681739. The next prime is 21681769. The reversal of 21681748 is 84718612.

It can be written as a sum of positive squares in only one way, i.e., 16744464 + 4937284 = 4092^2 + 2222^2 .

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 21915 + ... + 22882.

Almost surely, 2^21681748 is an apocalyptic number.

It is an amenable number.

21681748 is a deficient number, since it is larger than the sum of its proper divisors (20025190).

21681748 is a wasteful number, since it uses less digits than its factorization.

21681748 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 44823 (or 44810 counting only the distinct ones).

The product of its digits is 21504, while the sum is 37.

The square root of 21681748 is about 4656.3663945184. The cubic root of 21681748 is about 278.8462216160.

It can be divided in two parts, 2168 and 1748, that added together give a triangular number (3916 = T₈₈).

The spelling of 21681748 in words is "twenty-one million, six hundred eighty-one thousand, seven hundred forty-eight".