21351924 has 72 divisors (see below), whose sum is σ = 61090848. Its totient is φ = 6467040.

The previous prime is 21351919. The next prime is 21351943. The reversal of 21351924 is 42915312.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a plaindrome in base 13.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 9694 + ... + 11690.

It is an arithmetic number, because the mean of its divisors is an integer number (848484).

Almost surely, 2^21351924 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 21351924, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (30545424).

21351924 is an abundant number, since it is smaller than the sum of its proper divisors (39738924).

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

21351924 is a wasteful number, since it uses less digits than its factorization.

21351924 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2027 (or 2013 counting only the distinct ones).

The product of its digits is 2160, while the sum is 27.

The square root of 21351924 is about 4620.8142139671. The cubic root of 21351924 is about 277.4250491518.

The spelling of 21351924 in words is "twenty-one million, three hundred fifty-one thousand, nine hundred twenty-four".