21506644 has 12 divisors (see below), whose sum is σ = 38113600. Its totient is φ = 10617048.

The previous prime is 21506629. The next prime is 21506647. The reversal of 21506644 is 44660512.

It is a super-2 number, since 2×21506644² = 925071472285472, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21506647) 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, 33714 + ... + 34345.

Almost surely, 2^21506644 is an apocalyptic number.

It is an amenable number.

21506644 is a deficient number, since it is larger than the sum of its proper divisors (16606956).

21506644 is a wasteful number, since it uses less digits than its factorization.

21506644 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 68142 (or 68140 counting only the distinct ones).

The product of its (nonzero) digits is 5760, while the sum is 28.

The square root of 21506644 is about 4637.5256333523. The cubic root of 21506644 is about 278.0935282152.

The spelling of 21506644 in words is "twenty-one million, five hundred six thousand, six hundred forty-four".