21719640 has 64 divisors (see below), whose sum is σ = 66562560. Its totient is φ = 5667200.

The previous prime is 21719597. The next prime is 21719647. The reversal of 21719640 is 4691712.

It is a happy number.

It is a Harshad number since it is a multiple of its sum of digits (30).

It is a junction number, because it is equal to n+sod(n) for n = 21719598 and 21719607.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21719647) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 3715 + ... + 7565.

It is an arithmetic number, because the mean of its divisors is an integer number (1040040).

Almost surely, 2^21719640 is an apocalyptic number.

21719640 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21719640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (33281280).

21719640 is an abundant number, since it is smaller than the sum of its proper divisors (44842920).

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

21719640 is a wasteful number, since it uses less digits than its factorization.

21719640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3912 (or 3908 counting only the distinct ones).

The product of its (nonzero) digits is 3024, while the sum is 30.

The square root of 21719640 is about 4660.4334562356. The cubic root of 21719640 is about 279.0085684860.

It can be divided in two parts, 2171 and 9640, that added together give a palindrome (11811).

The spelling of 21719640 in words is "twenty-one million, seven hundred nineteen thousand, six hundred forty".