21155640 has 192 divisors, whose sum is σ = 73543680. Its totient is φ = 4857600.

The previous prime is 21155627. The next prime is 21155663. The reversal of 21155640 is 4655112.

It is a super-2 number, since 2×21155640² = 895122207619200, 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 21155640.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 450097 + ... + 450143.

It is an arithmetic number, because the mean of its divisors is an integer number (383040).

Almost surely, 2^21155640 is an apocalyptic number.

21155640 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 21155640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (36771840).

21155640 is an abundant number, since it is smaller than the sum of its proper divisors (52388040).

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

21155640 is a wasteful number, since it uses less digits than its factorization.

21155640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 114 (or 99 counting only the distinct ones).

The product of its (nonzero) digits is 1200, while the sum is 24.

The square root of 21155640 is about 4599.5260625417. The cubic root of 21155640 is about 276.5723263450.

The spelling of 21155640 in words is "twenty-one million, one hundred fifty-five thousand, six hundred forty".