21090644 has 12 divisors (see below), whose sum is σ = 37027284. Its totient is φ = 10511424.

The previous prime is 21090631. The next prime is 21090647. The reversal of 21090644 is 44609012.

It can be written as a sum of positive squares in 2 ways, for example, as 1993744 + 19096900 = 1412^2 + 4370^2 .

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21090647) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 7049 + ... + 9584.

It is an arithmetic number, because the mean of its divisors is an integer number (3085607).

Almost surely, 2^21090644 is an apocalyptic number.

It is an amenable number.

21090644 is a deficient number, since it is larger than the sum of its proper divisors (15936640).

21090644 is a wasteful number, since it uses less digits than its factorization.

21090644 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 16954 (or 16952 counting only the distinct ones).

The product of its (nonzero) digits is 1728, while the sum is 26.

The square root of 21090644 is about 4592.4551168193. The cubic root of 21090644 is about 276.2888001302.

Adding to 21090644 its reverse (44609012), we get a palindrome (65699656).

The spelling of 21090644 in words is "twenty-one million, ninety thousand, six hundred forty-four".