21640542 has 64 divisors (see below), whose sum is σ = 55738368. Its totient is φ = 5436000.

The previous prime is 21640537. The next prime is 21640547. The reversal of 21640542 is 24504612.

It is an interprime number because it is at equal distance from previous prime (21640537) and next prime (21640547).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21640547) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 13567 + ... + 15077.

It is an arithmetic number, because the mean of its divisors is an integer number (870912).

Almost surely, 2^21640542 is an apocalyptic number.

21640542 is a gapful number since it is divisible by the number (22) formed by its first and last digit.

It is a practical number, because each smaller number is the sum of distinct divisors of 21640542, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (27869184).

21640542 is an abundant number, since it is smaller than the sum of its proper divisors (34097826).

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

21640542 is a wasteful number, since it uses less digits than its factorization.

21640542 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1565.

The product of its (nonzero) digits is 1920, while the sum is 24.

The square root of 21640542 is about 4651.9395954806. The cubic root of 21640542 is about 278.6694612048.

The spelling of 21640542 in words is "twenty-one million, six hundred forty thousand, five hundred forty-two".