21437640 has 192 divisors, whose sum is σ = 81768960. Its totient is φ = 4769280.

The previous prime is 21437639. The next prime is 21437701. The reversal of 21437640 is 4673412.

21437640 is a `hidden beast` number, since 2 + 14 + 3 + 7 + 640 = 666.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 118350 + ... + 118530.

It is an arithmetic number, because the mean of its divisors is an integer number (425880).

Almost surely, 2^21437640 is an apocalyptic number.

21437640 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 21437640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (40884480).

21437640 is an abundant number, since it is smaller than the sum of its proper divisors (60331320).

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

21437640 is a wasteful number, since it uses less digits than its factorization.

21437640 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 252 (or 245 counting only the distinct ones).

The product of its (nonzero) digits is 4032, while the sum is 27.

The square root of 21437640 is about 4630.0799129173. The cubic root of 21437640 is about 277.7957888173.

The spelling of 21437640 in words is "twenty-one million, four hundred thirty-seven thousand, six hundred forty".