21181440 has 176 divisors, whose sum is σ = 77818752. Its totient is φ = 4816896.

The previous prime is 21181429. The next prime is 21181451. The reversal of 21181440 is 4418112.

It is a happy number.

It is an interprime number because it is at equal distance from previous prime (21181429) and next prime (21181451).

It is a Harshad number since it is a multiple of its sum of digits (21).

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 107422 + ... + 107618.

It is an arithmetic number, because the mean of its divisors is an integer number (442152).

Almost surely, 2^21181440 is an apocalyptic number.

21181440 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 21181440, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (38909376).

21181440 is an abundant number, since it is smaller than the sum of its proper divisors (56637312).

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

21181440 is a wasteful number, since it uses less digits than its factorization.

21181440 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 232 (or 214 counting only the distinct ones).

The product of its (nonzero) digits is 256, while the sum is 21.

The square root of 21181440 is about 4602.3298447634. The cubic root of 21181440 is about 276.6847103601.

Adding to 21181440 its reverse (4418112), we get a palindrome (25599552).

The spelling of 21181440 in words is "twenty-one million, one hundred eighty-one thousand, four hundred forty".