21638637 has 16 divisors (see below), whose sum is σ = 33943680. Its totient is φ = 13576896.

The previous prime is 21638633. The next prime is 21638647. The reversal of 21638637 is 73683612.

It is a happy number.

21638637 is a `hidden beast` number, since 2 + 16 + 3 + 8 + 637 = 666.

It is not a de Polignac number, because 21638637 - 2² = 21638633 is a prime.

It is a super-2 number, since 2×21638637² = 936461222435538, which contains 22 as substring.

It is a Smith number, since the sum of its digits (36) coincides with the sum of the digits of its prime factors.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21638633) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 23113 + ... + 24030.

It is an arithmetic number, because the mean of its divisors is an integer number (2121480).

Almost surely, 2^21638637 is an apocalyptic number.

21638637 is a gapful number since it is divisible by the number (27) formed by its first and last digit.

It is an amenable number.

21638637 is a deficient number, since it is larger than the sum of its proper divisors (12305043).

21638637 is a wasteful number, since it uses less digits than its factorization.

21638637 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 47169 (or 47163 counting only the distinct ones).

The product of its digits is 36288, while the sum is 36.

The square root of 21638637 is about 4651.7348376708. The cubic root of 21638637 is about 278.6612839466.

The spelling of 21638637 in words is "twenty-one million, six hundred thirty-eight thousand, six hundred thirty-seven".