21640220 has 24 divisors (see below), whose sum is σ = 51936864. Its totient is φ = 7419456.

The previous prime is 21640219. The next prime is 21640231. The reversal of 21640220 is 2204612.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 77147 + ... + 77426.

It is an arithmetic number, because the mean of its divisors is an integer number (2164036).

Almost surely, 2^21640220 is an apocalyptic number.

21640220 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21640220 is an abundant number, since it is smaller than the sum of its proper divisors (30296644).

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

21640220 is a wasteful number, since it uses less digits than its factorization.

21640220 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 154589 (or 154587 counting only the distinct ones).

The product of its (nonzero) digits is 192, while the sum is 17.

The square root of 21640220 is about 4651.9049861320. The cubic root of 21640220 is about 278.6680790458.

Adding to 21640220 its reverse (2204612), we get a palindrome (23844832).

The spelling of 21640220 in words is "twenty-one million, six hundred forty thousand, two hundred twenty".