21640244 has 6 divisors (see below), whose sum is σ = 37870434. Its totient is φ = 10820120.

The previous prime is 21640237. The next prime is 21640249. The reversal of 21640244 is 44204612.

It can be written as a sum of positive squares in only one way, i.e., 11155600 + 10484644 = 3340^2 + 3238^2 .

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21640249) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 2705027 + ... + 2705034.

It is an arithmetic number, because the mean of its divisors is an integer number (6311739).

Almost surely, 2^21640244 is an apocalyptic number.

It is an amenable number.

21640244 is a deficient number, since it is larger than the sum of its proper divisors (16230190).

21640244 is a wasteful number, since it uses less digits than its factorization.

21640244 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5410065 (or 5410063 counting only the distinct ones).

The product of its (nonzero) digits is 1536, while the sum is 23.

The square root of 21640244 is about 4651.9075657197. The cubic root of 21640244 is about 278.6681820643.

Adding to 21640244 its reverse (44204612), we get a palindrome (65844856).

The spelling of 21640244 in words is "twenty-one million, six hundred forty thousand, two hundred forty-four".