21690240 has 256 divisors, whose sum is σ = 82252800. Its totient is φ = 4792320.

The previous prime is 21690239. The next prime is 21690259. The reversal of 21690240 is 4209612.

It is a super-2 number, since 2×21690240² = 940933022515200, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (24).

It is a self number, because there is not a number n which added to its sum of digits gives 21690240.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 274521 + ... + 274599.

It is an arithmetic number, because the mean of its divisors is an integer number (321300).

Almost surely, 2^21690240 is an apocalyptic number.

21690240 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 21690240, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (41126400).

21690240 is an abundant number, since it is smaller than the sum of its proper divisors (60562560).

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

21690240 is a wasteful number, since it uses less digits than its factorization.

21690240 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 125 (or 113 counting only the distinct ones).

The product of its (nonzero) digits is 864, while the sum is 24.

The square root of 21690240 is about 4657.2781750718. The cubic root of 21690240 is about 278.8826217106.

Adding to 21690240 its reverse (4209612), we get a palindrome (25899852).

The spelling of 21690240 in words is "twenty-one million, six hundred ninety thousand, two hundred forty".