21085640 has 32 divisors (see below), whose sum is σ = 47770560. Its totient is φ = 8376000.

The previous prime is 21085621. The next prime is 21085643. The reversal of 21085640 is 4658012.

It is not an unprimeable number, because it can be changed into a prime (21085643) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 4295 + ... + 7785.

It is an arithmetic number, because the mean of its divisors is an integer number (1492830).

Almost surely, 2^21085640 is an apocalyptic number.

21085640 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21085640 is an abundant number, since it is smaller than the sum of its proper divisors (26684920).

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

21085640 is a wasteful number, since it uses less digits than its factorization.

21085640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3653 (or 3649 counting only the distinct ones).

The product of its (nonzero) digits is 1920, while the sum is 26.

The square root of 21085640 is about 4591.9102778691. The cubic root of 21085640 is about 276.2669474940.

The spelling of 21085640 in words is "twenty-one million, eighty-five thousand, six hundred forty".