21651924 has 72 divisors (see below), whose sum is σ = 61363008. Its totient is φ = 5913600.

The previous prime is 21651907. The next prime is 21651943. The reversal of 21651924 is 42915612.

It is a junction number, because it is equal to n+sod(n) for n = 21651891 and 21651900.

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 23 ways as a sum of consecutive naturals, for example, 12724 + ... + 14324.

It is an arithmetic number, because the mean of its divisors is an integer number (852264).

Almost surely, 2^21651924 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21651924, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (30681504).

21651924 is an abundant number, since it is smaller than the sum of its proper divisors (39711084).

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

21651924 is a wasteful number, since it uses less digits than its factorization.

21651924 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1645 (or 1636 counting only the distinct ones).

The product of its digits is 4320, while the sum is 30.

The square root of 21651924 is about 4653.1627953468. The cubic root of 21651924 is about 278.7183087166.

The spelling of 21651924 in words is "twenty-one million, six hundred fifty-one thousand, nine hundred twenty-four".