21209634 has 32 divisors (see below), whose sum is σ = 49184640. Its totient is φ = 6762096.

The previous prime is 21209633. The next prime is 21209653. The reversal of 21209634 is 43690212.

21209634 is a `hidden beast` number, since 2 + 1 + 20 + 9 + 634 = 666.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a junction number, because it is equal to n+sod(n) for n = 21209598 and 21209607.

It is not an unprimeable number, because it can be changed into a prime (21209633) 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, 7297 + ... + 9780.

It is an arithmetic number, because the mean of its divisors is an integer number (1537020).

Almost surely, 2^21209634 is an apocalyptic number.

21209634 is an abundant number, since it is smaller than the sum of its proper divisors (27975006).

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

21209634 is a wasteful number, since it uses less digits than its factorization.

21209634 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 17111 (or 17105 counting only the distinct ones).

The product of its (nonzero) digits is 2592, while the sum is 27.

The square root of 21209634 is about 4605.3918400067. The cubic root of 21209634 is about 276.8074182610.

Adding to 21209634 its reverse (43690212), we get a palindrome (64899846).

The spelling of 21209634 in words is "twenty-one million, two hundred nine thousand, six hundred thirty-four".