21601640 has 16 divisors (see below), whose sum is σ = 48603780. Its totient is φ = 8640640.

The previous prime is 21601639. The next prime is 21601667. The reversal of 21601640 is 4610612.

It is a happy number.

It can be written as a sum of positive squares in 2 ways, for example, as 20557156 + 1044484 = 4534^2 + 1022^2 .

It is a Harshad number since it is a multiple of its sum of digits (20).

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 269981 + ... + 270060.

Almost surely, 2^21601640 is an apocalyptic number.

21601640 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21601640 is an abundant number, since it is smaller than the sum of its proper divisors (27002140).

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

21601640 is a wasteful number, since it uses less digits than its factorization.

21601640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 540052 (or 540048 counting only the distinct ones).

The product of its (nonzero) digits is 288, while the sum is 20.

The square root of 21601640 is about 4647.7564480080. The cubic root of 21601640 is about 278.5023781770.

The spelling of 21601640 in words is "twenty-one million, six hundred one thousand, six hundred forty".